I'm getting involuntary visible muscle spasms all over, but in particular my forearm and biceps. i've been diagnosed with behets and now suspecting fibromyalagia as well. i am wondering are these spasms common in these conditions?

Brief comment: If you do indeed possess Behcets, peculiar that you would have a doctor diagnose "fibromyalgia", which is a description of pain often of unknown origin (perhaps a sleep disorder), and is often a wrong diagnosis. From your description, would suggest evaluation for small fiber neuropathy, or a myositis, or even metabolic or electrolyte dysfunction.