The crowd lynched the man following allegation of a pick-up van driver that the man had snatched money from him.
The victim Rupesh, who was brutally thrashed by a group of villagers, succumbed to his injuries in Patna during treatment.
Police have registered a case against one named and 150 anonymous people.
Rupesh Jha was assaulted by mob near Ramnagra village under Riga police station area on Sundat, following his altercation with the pick-up van driver.
He was first taken to the Sadar hospital and then shifted to the Patna Medical College and Hospital where he died.
Sitamarhi Sadar Deputy SP Veer Dhirendra told PTI that the reason behind the killing would be known after the investigation was over.
According to police sources, the pick-up van driver alleged that Jha was trying to flee on his motorbike after snatching his money and when he raised an alarm, the villagers assembled and beat him up with canes.
Jha's relatives, however, claimed that he was beaten up by the mob when he tried to overtake the pick-up van, the sources said.
Reacting to the incident RJD spokesperson Bhai Virendra said that there is a 'Maha Jungle Raj ' in Bihar.
There has been a spate in the incidents of mob-lynching in Bihar of late. In Rohtas, a middle aged woman belonging to scheduled class died after she was beaten cruelly by the residents of the area, over a minor feud between children. Before this, Begusarai lynching incident had come to light on Saturday where three were lynched to death for trying to kidnap a school girl.