A bag was noticed by the bus driver Monowar Hussain who on looking inside found the explosive, the sources said.
Without wasting time, he bravely snapped all the wires of the bomb connected with a battery and threw it at a corner of the bus stand, the sources said.
Police reached the spot immediately and covered the bomb with a blanket, they said, adding later it was taken to an open field where a bomb squad of the army safely defused it.
A piece of paper with 'National Liberation Forces of Bengali' written on it was recovered with the bomb by the police.
"An obscure name of an organisation having doubtful existence has been found at the site which would be clear only after investigation," Bongaigaon superintendent of police Abhijit Bora told reporters.
"Also the nature of the bomb could be ascertained only after analysis," he said.