Members of Rapid Action Battalion (Rab) in a drive arrested a fake Rab member from Jhalopara area of the city on Sunday afternoon.
The arrestee was identified as Md Rasel, 24, a resident of Kaistorail area of the city.
Rasel reportedly demanded extortion money from a factory of one Siraj Miah in the area in the afternoon introducing himself as a Rab members, said Nurul Islam, sub-inspector of Dakhshin Surma Police Station.
Later, locals caught the youth and informed Rab.
A team of the elite force arrested him and handed him over to police, added the SI.