Activist Agnes Chow of Hong Kong's democratization movement was released on Saturday after serving seven months in prison.
Media in the Chinese metropolis reported that Chow was taken to a car after her release and was not given the opportunity to speak to journalists.
Chow, 24-year-old, was convicted along with other prominent activists such as Joshua Wong and Ivan Lam for her involvement in protests at the Hong Kong police headquarters in 2019.
Protesters campaigned for months in 2019 against the Beijing government and the Hong Kong government.
The demonstrations started as a protest against a - now withdrawn - plan to allow extradition to mainland China, but grew into a broader call for more democracy.
Criticism of communist rule in Beijing has become much more difficult in Hong Kong since a new security law came into effect about a year ago.
Since then, important pro-democracy activists have been regularly persecuted.
Last week, authorities in Hong Kong banned another vigil to commemorate the victims of the 1989 Tiananmen protest. Hundreds of demonstrators were killed by the military on June 4 that year, when student protests in Beijing's Tiananmen Square were crushed. The organization's vice president, activist and lawyer Chow Hang-tung, was arrested.