I have numbness in right hand. What could be the cause of this?

Many possibilities. This can be carpal tunnel syndrome or compression of any of the nerves that go to your hand including compression up near the spinal cord. If this persists you should have it evaluated by a hand specialist.
Nerve compression. Numbness in the hands is usually secondary to nerve compression in the neck, shoulders, arms, or wrists. Carpal tunnel syndrome is the most common form of nerve compression in the wrists and can cause numbness in the fingers. An electrodiagnostic evaluation with a neurologist or physiatrist can be beneficial in diagnosing nerve compression.