What could a sharp pain on the head behind the ear indicate ?

Several options: If the sharp pain is triggered by touching or wind blowing on the area it might be a neuralgia of the occipital or upper cervical nerves. If it just happens without an inciting event and is very brief then it may be difficult to elucidate a cause. Sometimes it can be from muscle spasms in the area. If the pain becomes more constant or ear symptoms develop then see ent.