Three others were detained in the following days with the government saying at the time they had been held for their own safety.
Justice Minister Anisul Huq told AFP on Thursday that all six had volunteered to be in police custody.
“They came willingly. They said they wanted to go. They are allowed to return to their parents,” he added.
Hasina’s government restored order after deploying troops, imposing a curfew and shutting down the mobile internet network across the country of 170 million for 11 days.
More than 10,000 people were arrested in the wake of the unrest, according to local media.
“ARBITRARY AND UNLAWFUL”
Small and scattered protests resumed in cities around Bangladesh this week after other members of Students Against Discrimination ended a moratorium on demonstrations.
They vowed to restart their campaign after the government ignored a Monday deadline for their leaders to be freed.
“Their detention was arbitrary and unlawful. There was growing national and international criticism,” University of Oslo researcher Mubashar Hasan told AFP.
He added that the release of the leaders signalled the government was looking to “de-escalate tensions” with the protest movement.
Demonstrations broke out last month over the reintroduction of a quota scheme that reserved more than half of all government jobs for certain groups.