The chargesheet was filed in a court in Ara in Bhojpur district, 60 km from here, a lawyer said. Five of the six are in jail while one man is on the run.
A police official identified the six as Abhay Pandey, Sunny Singh, Ritesh alias Monu, Anil Pandey, Yogendra Pandey and Hare Ram Pandey.
Brahmeshwar Singh was shot dead in Ara town June 1 while on a morning walk. He founded the Ranvir Sena, an upper caste private militia that has been blamed for many killings.
The Bihar government formed a five-member special investigation team to probe the killing that sparked widespread violence. Later, the government recommended a CBI probe but the Central Bureau of Investigation is yet to take over the case.