A senior judicial magistrate’s court in Bogura sent Gazi Salauddin Tanvir, a former NCP joint member secretary, to jail on 5 August in a Cyber Security Act case.
Senior Judicial Magistrate Mehedi Hasan issued the order at the Bogura Sadar cognisance court.
The case was filed on 2 August by Bogura Sadar Upazila BNP president Maftun Ahmed Khan Rubel.
In the complaint, Rubel alleged that a Facebook post made on 29 July contained defamatory and provocative remarks about Prime Minister Tarique Rahman.
The complaint further alleged that the post was shared online and caused confusion and tension among the public.
Tanvir subsequently removed the post and expressed regret.
Bogura Sadar police said Tanvir was arrested in Dhaka on Tuesday, but the reported timing and location differ.
One police account placed the arrest at about 4am in the capital, while another placed it at night in the Monipur area of Dhaka.
NCP temporarily relieved Tanvir of his central joint member secretary role on 1 August and asked him to provide a written explanation within two working days.
The party said his social-media remarks had harmed its image and breached organisational discipline.
The alleged post followed claims of attacks on NCP road meetings in Sylhet; one account also referred to an alleged attack in Habiganj.