A huge crowd had gathered at an outdoor venue for the burning of effigies at dusk, part of the Dussehra festival.
Officials said the stampede happened as people were leaving at the end of the event. Television channels quoted a witness as saying there were not enough lights when the ceremony ended.
At least 15 injured people were taken to hospital, police chief P.K. Thakur said. Police are examining closed circuit television to determine what had triggered the stampede.
“There was very little police presence and there were vendors who had put up their stalls at the exit gates, making it more difficult to leave,” a witness told NDTV.
Patna police superintendent Prantosh Kumar Das said some people reported that had they heard a rumour that a live electric wire had fallen on the public ground and it quickly spread through the crowd, prompting a rush for the gates.
Television showed shoes, slippers and handbags strewn over the ground.
Dussehra is one of the biggest Hindu festivals celebrating the victory of good over evil from the epic Ramayana. (Reuters)