My brother constantly chews his lower lip, is it an ocd? What can be done about it?

No. Lip chewing or lip biting is a habit, which may be associated with anxiety, but is often simply a habit along the lines of skin picking, hair twirling, and nail biting. Ocd stands for obsessive-compulsive disorder, which is characterized by significant impairment and dysfunction, whereas the habits listed above generally, in and of themselves, do not cause significant impairment.
Nervous habit. Your brother's lip chewing is more likely a nervous habit than ocd. The o in OCD refers to obsession and the c refers to compulsion. The most common compulsions are hand washing and checking behaviors. Repetitive handwashing is due to an obsessive fear of germs and disease. Your brother"s lip chewing is probably no different than the nail biting many people do. Behavioral therapy can help.