Don't make a big deal about it, and it will pass. My son will be 3 in May and at about 2 1/2 years he started to stutter as well. We were at our Pediatrician for my other son that same week and so I asked him on the side, (not wanting to let my 2.5 year old know I was concerned).
He pretty much said that it was his brain thinking SO fast that his mouth couldn't keep up. We would totally notice it more if he was more excited too. Anyway, I totally believe that was the case. He has been learning so many new things so fast...he couldn't ask new questions fast enough, or tell Daddy what he had done that day, fast enough. Does that sound like your little boy?
Anyway, the Doc said to leave it alone and not to make a big deal about it, and it will pass, and it pretty much has. We rarely hear it anymore...unless he is SUPER excited. Good luck!