The IED was found amidst the stones between the tracks by patrolling railway police at Barigaon this morning.
The bomb disposal squad of the Army has been informed and the IED was expected to be defused by this evening.
All trains in the Jogighopa-Guwahati line have been suspended since 9 AM and were expected to resume by this evening, railway officials said.
The weight of the IED was yet to be ascertained, the police added.