The operators of the June 4 Museum were on Tuesday fined HK$8,000 for running the venue as a place of public entertainment without the required licences.
The Hong Kong Alliance in Support of Patriotic Democratic Movements of China was prosecuted by the Food and Environmental Hygiene Department for committing the offence between May 31 and June 1 this year.
At Kowloon City Magistracy, the lawyer representing the alliance pleaded for a lenient sentence on Tuesday, noting the group was willing to pay a fine.
She added that the museum in Mong Kok was not run for profit and at the time officers inspected it, only around 20 visitors were there, with two staff members on duty.
The lawyer also noted that the alliance closed the museum after it was prosecuted.
Magistrate Jacky Yip ordered the alliance to pay the fine within a month.
The maximum penalty for first offenders in such cases is a fine of HK$25,000 and six months imprisonment.
The museum first opened to the public in 2014 and the alliance had wanted it to be a permanent venue.
It held exhibitions on different themes related to pro-democracy movements on the mainland and in Hong Kong, but shut down in 2016 after a legal dispute over the fact it was located in a building designated for office use.
The museum reopened on May 31 but closed again a day later.
The alliance said it had sought legal advice and decided to close the museum “until further announcement”.