Police arrested Mr Khan on Saturday over allegations that he spread false information about the government.
Mr Khan published a report on violence during a protest by hard-line Islamists in May in which several people were killed when police opened fire.
He is a known as a high-profile critic of alleged abuses by security forces.
The government consistently denies such allegations and says it has the right to take action against those who it describes as involved in anti-state campaigns
“The arrest of Adilur Khan appears to be an attempt to silence one of the Bangladeshi government’s most vocal critics prior to national elections,” Brad Adams, Asia director at Human Rights Watch, said in a statement.
Mr Khan worked for the Bangladeshi rights group Odhikar. It was in a report for Odhikar that he challenged the government’s version of events of the deadly crackdown on a protest in May.
After his arrest on Saturday he was remanded in police custody for five days for questioning.