If it's a laptop it's not easy to see/clean, if it's a desktop the easy way is to buy a new keyboard and try it, i guess you can find one for less than 10 bucks (well, at least in Italy keyboards are cheap).
If the new k/b does the same i think it should be a software related issue (not very likely to happen).

If your computer is an Apple you will have to pay a little more for the keyboard.

Hope this helps

Mauro.