The three -- Mainul Ali, Sahidul Ali and Rubul Ahmed -- were apprehended from Mirza under Palashbari police station while they were traveling in a car.
One pistol, two rounds of ammunition, four mobile phones and extortion notes, besides the car, were seized from them, the sources said.
They were being interrogated at the Palashbari police station.
However, the police were yet to reveal to which extremist group the trio belong.
