Malik Z. Shabazz, the president of Black Lawyers for Justice, based in Washington, filed the federal lawsuit seeking $41.5 million on behalf of five protesters arrested between Aug. 10 and Aug. 13. He said he expects more plaintiffs to come forward.
Shabazz called the response to the demonstrations "virtually a police riot."
"Police were out of control," he said, adding that "excessive force" was used frequently.
The death of Michael Brown, 18, an unarmed black teenager shot by a white police officer set off large protests. Police responded with a show of force, including military vehicles and weapons.
Thousands of people attended Brown's funeral Monday.
Tracey White, one of the plaintiffs, said she and her son were arrested at a McDonald's in Ferguson on Aug. 13 as they waited for her husband. She said officers with rifles stormed the restaurant.
"It looked like something out of a movie. It was so horrifying," she said.
White said she and her son were arrested for "failure to disperse" and released a few hours later. She said police knocked her down when they detained her.
The city and county police chiefs are also named as defendants along with police officers.