Truck entrepreneurs and locals have captured and thrashed Babu Thapa, the central vice-chairman of the Chure Bhawar Ekta Samaj and the coordinator of the talks team.
They later handed him over to the police on Friday. Thapa is in police custody, The Himalayan Times daily quoted inspector Gautam Raj Kattel of the Simara police office as saying.
Locals had also beat up Thapa before handing him over to the police.
Meanwhile, three activists of the Society were injured when police opened fire in Sarlahi Friday morning.
Police said they opened fire in self defence after the protesting activists attacked them.