HONG KONG—Police arrested three prominent opposition activists as authorities cracked down on dissent ahead of an anticipated 13th weekend of protests in the city, a move that could give new energy to the movement.

Joshua Wong, a leading pro-democracy campaigner who is secretary-general of the youth political group Demosisto, was taken into custody Friday morning on his way to a subway station near his home, Demosisto said. Police pushed 22-year-old Mr. Wong into a private car on the street and he was