My 3-year-old son stutters a lot while talking, especially when he is very happy or excited. Is it normal or should I visit a specialist?

Yes, if he does it lot often you must see a specialist. May be there is noting and it will go on its own but it is always better to take the expert's opinion. You know one of my cousins stutters the same way when he used to be excited but his parents never thought it too serious to show to a doctor. But as he grew up, his strutting also reduced. I mean you could still see him excited but he doesn't stutter.