Police said the three, Gokul Lahan, Ganesh Lahan and Dijen Buragohain, all hardcore ULFA ultras, hailing from upper Assam's Sibsagar district, had entered the district last night with explosives for engaging in subversive activities.
Acting on a tip-off, the army and police managed to nab them from Dhekialuci area in the early hours today.
The RDX was recovered from them and seized by the security forces.
The arrested ultras admitted they were planning subversive activities in the district, police said.
In another incident, police recovered the bodies of two teachers, Kamaleswar Rabha and Sarit Rabha, who were kidnapped last month from Golpur area of the district.
The teachers were kidnapped by local miscreants who shot them dead after their ransom demand was not met, the sources said.