The incident took place in Chak village in Chandauli, where a group of locals attacked the five-year-old leopard. The animal died after suffering multiple injuries.
"It is yet to be established whether the villagers killed the animal for self-defence or for any other purpose," Divisional Forest Officer P.P. Singh told reporters here.
"We have initiated a joint enquiry into the case with a police team. All those involved in the killing of the leopard have been booked under the Wildlife Protection Act (WPA)," he added.
Killing a leopard is a serious crime under the Indian Wildlife Act. The offenders can face three to seven years' rigorous imprisonment if they are found guilty.
Forest officials are yet to ascertain whether the leopard came from the adjoining forest area of Bihar or from forests in Uttar Pradesh.
"The forest area of Bihar is just 10-12 km away from the spot where the leopard was killed," Singh said.