My cat does this too!! I did take him to the vet but nothing could be found obviously wrong with him. They suggested Hill's diet for allergens (forgot which kind) but instead of doing that I switched to a high quality diet. The effects were evident almost instantly. He does still lick alot on his belly but he has no dandruff anymore and is now a healthy weight (was 17lbs and now is 14lbs). Good luck.
Note of caution: When you take him to the vet they will probably suggest Hill's Science Diet food. DONT buy it. Sugarcatmom is an expert on feline nutrition (she helped me) so please talk to her about what to feed.
Some brands I use--
I dont know where you live but around here at Petco you can find alot of these brands otherwise just do a google search.