Hi,
Nearly all 3 year olds are very active and impulsive; that's the nature of being a pre-schooler. However, there are some who are way more active than others and it could be a sign that he is hyperactive or even have ADHD. Not all children who are hyperactive have ADHD; they could be anxious, for example or even suffer from allergies that make them "antsy." Some gifted pre-schoolers are very active, too. There are a lot of reasons why a child at 3 can be extremely active.
Does his pediatrician have concerns? Do his teachers feel he is more active than the average 3 year old? What was the recommendation of the doctor who felt he was a bit hyperactive?
If there is a concern, you might want to consider a formal evaluation. It is tricky finding clinicians who evaluate such young children, but they can be found. Try contacting the Children's Hospital nearest you or a teaching hospital with a pediatric department and ask for someone with a lot of experience in evaluating pre-schoolers for possible ADHD.
Hope this helps!
Terry