Milon Hossain, a teacher of Piyar Ali School and College, was whisked away on Saturday night, bdnews24 reported.
Milon was produced before a court that granted police five days to investigate him in custody, a police officer said.
Milon, who hails from Lalmonirhat, worked at Madbar Memorial School in Ashulia area near Dhaka.
Milon had helped Ujjal get a job as a teacher at the school, the officer said.
Ujjal was among six attackers killed by security forces to free the cafe siege hostages.
The Islamic State terrorist group published photos of five gunmen and claimed they killed over 20 persons in the cafe, bdnews24 reported.
Ujjal, a madrasa student from Bogra, was among the five “IS fighters”.
He had left home six months before the attack, his family said.
At least 22 persons, including an Indian women were brutally killed during the siege on July 1 in the popular hangout, Holey Artisan Bakery and O’Kitchen Restaurant, in Dhaka’s Gulshan area.