What does it mean when an mra shows the intracranial right internal carotid artery is narrowed?

Depends on degree. An mra can show a area of mild to severe narrowing. Usually this means that there is focal atherosclerosis of the vessel. The consequence of the narrowing depends on how narrow the vessel is, where the vessel is, and if there are alternative routes for blood to use to reach the area of the brain affected by the narrowed blood vessel.