The incident occured near Dharmpur village as a pick up van with scores of passengers, lost control and overturned killing three persons on the spot, while 15 others sustained injuries, the Superintendent of Police (SP) Kumar Ashish said.
The bodies have been sent for post-mortem and the injured admitted to Sadar hospital for treatment, he said.
Efforts were on to ascertain identity of the victims, Ashish added.
The ill-fated vehicle was returning to Bergama village after the Tilak ceremony of one Kamlesh Ravidas's daugh ter at Rajgir, the SP said.