The Demosisto organization released a statement noting that "secretary-general" Wong had been arrested and allegedly "forcefully pushed into a private minivan" on his way "to the South Horizons MTR station."
Earlier, Chinese media reported that Wong, who was accused by the government of colluding with overseas anti-China forces to smear the image of China and the Hong Kong Special Administrative Region, met with Julie Eadeh, political unit chief of the US consulate general in Hong Kong, on 6 August.
In 2014, Wong was the most public face of Hong Kong's protest movement. He was sentenced to community service for unlawfully entering the forecourt of a government building dubbed Civic Square, that at the time was closed to the public.
During the mass Umbrella Revolution, demonstrators occupied busy intersections across Hong Kong and attempted to storm the Hong Kong government headquarters. Government officials described the occupations as unlawful, and a number of activists were detained. Demonstrations lasted for 79 days before the last remaining occupied areas were cleared by police.
Following the reported arrest of Wong, Demosisto announced that another of their members, Agnes Chow, had been arrested.
In early June, the mass protests in Hong Kong were initiated by proposed amendments to the city's extradition laws but over several months grew into a full-blown opposition movement against Beijing's tightening grip on city affairs.
Recently, the level of violence during the protests has gone up, according to government statements, even as both sides employ increasingly aggressive tactics.
Chinese Foreign Minister Wang Yi has called the recent massive protests in Hong Kong the most serious since the region's return to China in 1997.