Well?
In “The Day the Earth Stood Still” it was Klaatu’s command to Gort (the robot) NOT to destroy the Earth. Gort, BTW, was played by the head doorman of Graumanm’s Chinese Theater and he was so weak that they had to use a double for him to pick up Patricia Neal.
“Keep looking to the skies!”
It’s from the movie “The Day the Earth Stood Still” (1951).
It’s the alien’s command to his robot, Gort, not to destroy the Earth. If it wasn’t given to him in time, he would carry out his destroy orders. Patricia Neal eventually has to race across Washington, DC (while passing all the monuments :)), to the White House and say it to Gort.
Dang! I had the reply all ready, but kept getting interrupted before I could his Submit. 
Since you give no details as to where you heard it, I’m going to assume you were told this totally out of context.
In the 1951 movie “The Day the Earth Stood Still,” Klaatu is the humanoid alien that lands in Washington with the robot Gort. He tells the humans that they must stop their warlike ways, or Gort will be forced to destroy the planet. His people don’t want a dangerous race to mature and infect the galaxy with our craziness.
Klaatu is befriended by an Earthwoman, Helen Benson. When the trouble starts (humans start acting like they might think they can take him and Gort on), he tells Helen what to do if Klaatu is hurt or killed. If that happens, Gort will blow up the Earth, unless he is commanded not to. Helen must say, “Gort, Klaatu barada nikto,” to the robot.
Klaatu is of course shot, and she says the words to Gort. Gort grabs the body, reanimates Klaatu, and they leave, saying they’ll give us a few years to get our act together. Otherwise, they’ll be back to take us out.
So, the answer to the OP is that it means, in some alien tongue, “Klaatu doesn’t want the planet atomized, and he’d like you to bring him back to life, if you’d be so kind.”
When I watched the movie “Army of Darkness” and they told Ashe that he needed to use the magic words “Klaatu Barada Nikto,” myself and my three friends were the only ones in the packed theater to laugh. These kids today, they just don’t know their classic SF.
The movie was very loosely based on the Harry Bates short story, “Farewell to the Master.” Read it if you get the chance.
I just previewed, and see that others were faster. But I’ll post anyway, in case anyone wants my unnecessary details.
Thanks all. In case you were wondering what promted my question, Cecil mentions this phrase in in his column on stopping telemarketers which is on the SD classics link today.
Given Klaatu’s nearly Jesus-like patience with Terrans, I am inclined to think that Gort, Klaatu barada nikto. means more like; Gort, Klaatu is hurt, help him.
“Klaatu barada n(cough, cough, cough, cough).”
Good movie, particularly the amazing shotgun which holds at least two dozen shells in its nonexistent magazine.
Well WAG has always been, “Klaatu lives nomore”. It was only three words so it should translate to three words. Since Helen is delivering a message in Klaatu’s native language, the message must have been given to her by Klaatu and this proves she if a friend so that’s why Gort doesn’t hurt her. Next, Gort is smart enough to realize the Klaatu would like to be revived so he does that. Once Klaatu is back he can give Gort any further orders.
[slight hijack] A while back, there was an aura of mystery surrounding the musical group Klaatu, IIRC. Has the veil ever been lifted? [/slight hijack]
Ummm, why?
Take for example, the German word, schaudenfreude (probably not spelled correctly). Try to make a one-for-one translation into English.
I think K.B.N. means “Klaatu says ‘ixnay on the estroyday.’” 
It’s from the classic John Huston film Treasure of the Sierra Madre (1948).
When the bandits enter the miners’ camp, they claim to be police agents, and Fred C. Dobbs (Humphrey Bogart) says “If you’re the police, then show us your badges!” And Gold Hat says “Klaatu Barada Nikto.”
You sure about that Uke? I always thought “Klaatu Barada Nikto” was the name of Charles Foster Kane’s sled.
Well at least I can slide in here and be the first to mention that the quote is also seen in the background on a cubicle wall in the movie TRON.
Well, Cabbage, it WAS a kind of catch-phrase around Hollywood. Sorta the “Show me the money!” of its day.
Who could forget the moving finale of King Kong, where the poice officer says “Well, the airplanes got him!” and Carl Denham says “No…Klaatu Barada Nikto.”
Or that great scene in Casablanca: “Play it, Sam. Play ‘Klaatu Barada Nikto.’”
This one predates even Hollywood, gentlemen, but it was revived there. Haven’t you ever read your Shakespeare? Remember the scene in Julius Caesar, right after everyone has stabbed Caesar? He looks up from the ground, his life ebbing away, and to his best friend, Brutus, he says, plaintively:
“Klaatu barada nikto.”
I imagine it has some Latin meaning.
LL
I knew the reference! 
I love Army of Darkness. Bruce Campbell and Sam Raimi always make a great team together.
-Ashley