it may be worth mentioning that if this is a new guitar and thereby has new strings on it, they may just be getting stretched out. New strings stretch fairly quick and buzz until they're "broken in". Do you find yourself tuning the guitar a lot?

Chances are that one of the answers above is the right one, but I remember when I first started playing guitar I was mad because my strings were buzzing (acoustic), but after playing for a few days, it was gone.