This is a very common font but I can't remember it. I saw it suddenly on my keyboard just now. The image actually doesn't appear clear until you zoom in on it.
(I tried automatic font-ID sites but as the picture is of a keyboard, they failed).
Did you try Montserrate. I love this font and currently creating a website using the same font. I'm sure this is the most closest font with this one..
but I searched through http://www.identifont.com/ for you.. and found.
Following list of matching fonts..
in the above link.. check left list. one by one and on the right.. closet matching fonts.