Baby "spit up"
All babies have a certain ammount of "spit up" that resolves over the first 6 months of life.
As long as a baby gains weight, is happy and developing normally it should not be a problem. Make sure you do not over feed your baby, and that you do not rock him or put him in a swing after feeds. Keep your baby in his infant seat for about 30 minutes after feeds, it will keep him at an elevated angle.