Is it an electric? Does the buzz amplify? A little rattle is normal on electrics.
If you are just buzzing when fretting the 1st fret, then either fret 1 is low or 2 is high. get a short straight edge and see if it rocks when you straddle 1, 2 and 3. It should be level. If it rocks, figure out which one is high and consider filing it down, a very little at a time.