The incident occurred around 11:30pm on Wednesday
No one has been arrested over the haul.
Bangladesh Border Guard (BGB) said that the Joypurhat-bound bus was searched on a tip-off.
"Around 3.6 kilograms of gunpowder have been found," said Joypurhat-based BGB-3 Battalion's Operation Officer Major Ashraf Ali.
He said that no one had been detained over the seizure.