If he's young (under six months), it's pretty normal. My dwarf hamster has a cage that's the recommended size of 360 square inches. A lot of what she does is run on her wheel or dig in her 10″ pile of bedding. However, if you have a cage like this: then I'd expand. read more
A hamster in the wild would run about 7 miles in a single night - which is a lot of running for a little creature only about 4 inches long! In a small tin or plastic cage, his wheel provides him with his only opportunity to do the running activity that his body instinctively wants to do. read more