Officers formed a human barrier outside Colindale police station after protesters gathered over the arrest of a 14-year-old boy.
In a statement, Metropolitan Police said officers arrested the teenager on suspicion of possessing cannabis following a stop and search.
During the arrest, a group gathered around the officers and a further two men, aged 23 and 25, were arrested on suspicion of obstructing police.
The officers then left the scene in a car and were followed on foot by 40 people to Colindale police station, the force said.
The protesters proceeded to demonstrate outside the station, demanding the release of the teen and the two men.
A cordon was put in place around the station and police authorised a Section 35 dispersal order preventing members of the public from gathering outside the station. The order will stay in place until Sunday.
In a video posted to Twitter, Temi Mwale, director of youth group 4FrontProject, claimed that two members of her staff had been arrested by police.
Ms Mwale appealed to members of the public to join the protest outside the station.
"This community is sick and tired of the way we are being treated, now we need your support," she said.
"They have disappeared members of our community, they have disappeared young people, they have disappeared community workers."
4FrontProject describes itself as a member-led youth group empowering young people and communities to fight for justice. They are involved in the organisation of a Black Lives matter protest taking place in Tottenham on Sunday.
One witness said protesters blocked access to Colindale police station, and refused to allow police vehicles to pass.
The 14-year-old was released under investigation with his mother present.
