Prime Minister Sheikh Hasina's government has blamed the homegrown JMB and another group called Ansarullah Bangla Team (ABT)
An Islamic spiritual leader and an explosives expert were among the group detained in a series of raids in the capital late Wednesday and early Thursday, the Rapid Action Battalion (RAB) police unit said.
"They belonged to Sarwar-Tamim group of the Jamayetul Mujahideen Bangladesh (JMB)," RAB said in a statement, referring to the extremist group the government has blamed for the July attack.
RAB said a 27-year-old electrical engineer who made explosives for the group and provided training, and a 40-year-old spiritual leader who preached Jihad to the group's budding extremists were among those arrested.
The Islamic State group and Al Qaeda in the Indian Subcontinent claimed responsibility for the siege at Holey Artisan Bakery cafe in Dhaka's posh Gulshan neighbourhood.
But Prime Minister Sheikh Hasina's government has blamed the homegrown JMB and another group called Ansarullah Bangla Team (ABT).
The leader of the JMB, Sarwar Jahan, and the mastermind of the cafe siege, Tamim Chowdhury, a Canadian citizen of Bangladeshi origin, were both killed in raids outside the capital by security forces in recent months.
The July carnage triggered a security force crackdown on Islamist extremists, with police shooting dead nearly 40 suspected militants and arresting scores more since.