Why does my right calf feel numb like it is asleep?

Nerve problem. You probably have a problem with the nerve that goes to that part of the leg. It can either be from the spine, or it could be a problem in the nerve just below the knee. If you are just having this symptom, and no other pain, it is probably nothing to worry about. If you notice weakness in the muscle, or worse pain with coughing, then it could be from the spine. See a doctor if that is the case.