The four insurgents, including two in NIA list, were held when they were coming from Meghalaya on Monday night, police officials said.
They were identified as NDFB(S) 'Commanding Officer (CO)' Lankeswar Bodo alias Lachi, 'deputy CO' Santosh Kherkotari alias Chimang and two cadres Rabiram Basumotary and Gambar Gayari.
Lachi and Chimang were involved in the Narayan Guri Massacre in 2014 and their names were in the NIA list for some murder cases in Narsingbari in the same year.
The arms included one AK-56 rifle with magzine, 82 rounds of cartridges, two grenades, one pistol, two detonators and 10 kg RDX explosive.