“Si” is rarely used in Quebec French, but yes, it does indeed mean what Noone Special says it does. I don’t know if it is more widely used in other francophone countries, maybe clairobscur or someone else can tell us.
Of course, “si” also means “if”, among other things, but in this case it’s a conjunction, not an adverb.
heh, and I call myself bilingual. Still, I have a feeling that if I were to use “si” like this at work, people would look at me funny and/or ask me if I actually speak Spanish or something! Good to learn something new, though - it doesn’t happen every day!