The singer's cousin Alpha L. Walker and his girlfriend Tamara Diaz are accused of trying to extort the Grammy-winning musician over a videotape that portrays Wonder negatively.
Walker's attorney says his client simply made a movie about his life and his actions are protected by the First Amendment.
The two were arrested in May after receiving $10,000 from Wonder's attorney in a police sting.
The Associated Press contributed to this report.
