Hi, yes, he could have a cradle cap type of situation or psoriasis of his scalp. A trip to the doctor would help determine that. they do some special treatments to the scalp and he'd use a special shampoo.
And yes, it could also be an anxiety disorder. I've known people to pull every hair out of their head without thinking about it as part of their obsessive compulsive disorder). Again, a doctor is essential for that.
good luck and let us know if you follow up with your doctor what he says.
Does he have a rough spot there that is flaky or crusty, so it attracts his attention? Some people have one or more of these, and they either itch or just feel rough and if so it's not easy for them to leave them alone. If he is doing it to a normal, smooth scalp that has nothing on it, I don't know what to advise although possibly if you gave him a multivitamin he would tend to pick less. (Sometimes people do compulsive behaviors, like chewing ice, out of a vitamin deficiency.)