A joint team of army and police during routine patrolling recovered the grenades kept wrapped in a polythene bag under the seat of an Assam State Transport Corporation (ASTC) bus on its way to Tezpur from Guwahati.
The grenades were being carried by two suspected ULFA militants, who boarded the bus from Baihata Chariali in Kamrup (Rural) district, the police said.
The police arrested one of them, while the other managed to escape.
The arrested has been identified and is suspected to be a member of Paresh Barua led ULFA's anti-talk faction.