One person identified as Jahar Ahmed, a resident of Kaliachak in Malda district, was arrested during the joint raid by CID and GRP as the train was about to leave, a top GRP official said.
The firearms were hidden under the seat.
Police grilled Ahmed to find out if he was part of any arms racket and if the weapons had any link with the coming elections in north Bengal.
In the second phase of polls, there will be voting in Raigunj, Malda North and South, Balurghat, Jangipur and Murshidabad on April 24.