Alpha Lorenzo Walker and girlfriend Tamara Eileen Diaz were charged in May with felony extortion for an alleged plot against the singer.
Walker, a cousin of the singer, and Diaz apparently demanded money not to release a video which apparently paints Wonder in an unflattering light.
Both suspects have now formally entered not guilty pleas, the LA district attorney told The AP.
Their lawyer has claimed that the video was simply a movie about Walker's life, which he said should be protected by the First Amendment.
Walker and Diaz will return to court in the coming weeks as the case proceeds.
Wonder has not spoken publicly about his cousin's not guilty plea as yet.
Watch Stevie Wonder perform 'I Just Called To Say I Love You' below: