RAB claimed 52-year old Moinuddin Bhuiyan Biplob, a resident of Moghbazar, was a drug addict.
Operations Officer Md Saiful Islam said they had raided a house at Peyarabagh on Thursday night and arrested three men along with Biplob with 68 pieces of the contraband yaba tablets.
The three had been caught while doing the drug, he said.
According to the RAB officer, Biplob collapsed in front of the others and doctors at a local clinic declared him dead when he had been rushed there minutes later.
RAB officer Islam claimed Biplob's family said he had been suffering from heart-related diseases.
"But he collapsed mainly due to 'fear'," he said.
Ramna Police Station's OC Moshiur Rahman said a case was being lodged in connection with the incident.
A post-mortem examination would reveal the cause of his death, he said.