CNN reports Hong Kong media tycoon Jimmy Lai was arrested early Monday.
Lai is known for his support of the city's pro-democracy movement and criticism of China.
The arrest comes under the new security law imposed on the city last month by Beijing, which bans "collusion with foreign forces."
The Hong Kong Police Force say seven people were arrested, aged 39 to 72.
Charges against them include collusion with foreign forces to endanger national security, and conspiracy to commit fraud.
While it isn't the first time Lai has been arrested for political activities, this latest arrest is among the first since the security law was imposed on July 1st.