The arrest comes after China imposed a sweeping new national security law on Hong Kong in late June.
Disqualified candidates included activist Joshua Wong, some members of the Civic Party and others who won an unofficial primary vote held by the opposition camp earlier this month.
Chan Kin-man was found guilty last year of conspiracy to commit public nuisance for his role in planning and mobilising supporters during the 79-day protest that brought parts of the Chinese-ruled city to a standstill.
Thousands of protesters, many wearing masks and reindeer horns, gathered on the streets after scuffles in shopping malls on Christmas Eve. The protests against China's control over the territory are now in their seventh month.
Government supporters took to the streets of downtown Hong Kong after a chaotic working week saw hardcore anti-Beijing activists cause widespread disruption in the city and stretch police resources.
Wong became the poster child of the huge pro-democracy "Umbrella Movement" protests of 2014. Wong and his party, Demosisto, have denied supporting independence for the city.
More than 100 people were injured during Tuesday's turmoil, the hospital authority said, as angry demonstrators took to the streets across the territory and police fired tear gas and water cannons to try to disperse them.
Carrie Lam faces more than two hours of grilling at a public "dialogue session," the first time her pro-Beijing administration sits down with its critics in 16 consecutive weeks of unrest.
Anti-Beijing activists urge members of the US Congress to pass legislation to combat alleged human rights abuses in Hong Kong.
The operator of the express train to Hong Kong's airport has suspended service as anti-Beijing protesters gathered there following a day of violent clashes with police.
China's ambassador to the United Kingdom said Beijing would use its power to quell Hong Kong protests if the situation deteriorates further.
The US president linked a humane resolution to anti-Beijing protests to China trade deal in tweets as Hong Kong activists plan more mass rallies this weekend to show their movement maintains public support despite disruptive sit-in at the airport.
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