My 4 mo. Old keeps getting little dry spots on his head. What are they and is he okm?

Cradle cap? Cradle cap presents with dry flaky spots on head, can treat with selenium containing shampoo (dandruff shampoo).
Seborrhea. Sometimes infants get scaly patches in the scalp-which is seborrhea or "cradle cap". Most of the time it gets better by itself. However, there is an easy remedy to clear it faster- a small amount of baby oil rubbed into the scalp followed by gentle rubbing with a baby comb to loosen the scale. You can wash the scalp afterward with a gentle, hypoallergenic wash.