There are numerous temples dedicated to Bhairava in Nepal in which only the head of Bhairav is worshipped. So what is the reason for worshipping beheaded Bhairava deity?
Legend has it that Bhairava, the guardian deity of Kashi or Varanasi, traveled to Bhaktapur in Nepal to witness the Bisket Jatra.
A high priestess of a temple in the region recognized Bhairava and attempted to capture Him. Bhairav tried to escaping by making hole in the ground. To prevent His escape, the priestess ordered His head to be cut off where it protruded from the ground. This head was worshipped in a Bhairav temple in the region. The body returned back to Kashi or Benares. It is believed by people this region of Nepal that only body of Bhairava is worshipped in Kashi.
In some stories it is Kashi Vishwanath himself who visited the jatra.