Yes could be itching so definatly get that checked out, if it is behavioral, is he upset about anything have there been any changes in his life could have upset him?It could be a way of getting attention, yelling ,will not solve it,if anything it gets him attention even negative attention, Does he get to plenty of outside activities is Dad involved in Games and sports with him.Check out what factors could be making him do this.
Our son did this when he was five years old. My dear neighbour suggested that he might have pinworms. So, I went to the pharmacy and asked for the medication (in our area it is behind the counter but not prescription and so one has to ask the pharmacist for the medication). Sure enough, within a short time the behaviour stopped. Perhaps this is the problem with your son.