Brown is charged with breaking the nose of a 20-year-old Maryland man who tried to get a picture with him in October. His bodyguard, Christopher
Hollosy, faces the same charge.
A lawyer for Brown, Danny Onorato, told reporters the deal had been turned down because "Chris Brown's not guilty."
He said he expected a date for a trial at the District of Columbia Superior Court to be set at a February 20 hearing.
Prosecutors offered Brown, 24, a plea deal that required him to plead guilty to simple assault.
During the 10-minute hearing, Brown and Hollosy appeared relaxed and chatted with attorneys. Brown smiled several times.
Facts of the argument that led to the charges are disputed.
A police report said the man who was punched had sought a photograph with Brown. Other witnesses said the man tried to force his way onto Brown's tour bus.
Brown's attorneys say his bodyguard was trying to protect him when the altercation arose.
Prosecutor Nicholas Cannon told Judge Yvonne Williams he still was compiling evidence against Brown.
"We have video surveillance," he said. Cannon gave no details of what the video showed.
In 2009, Brown was sentenced to five years' probation, community labor and domestic violence counseling after assaulting then-girlfriend Rihanna.
Brown's probation was revoked by a Los Angeles judge last month following the Washington fracas. He was not taken into custody because of good reports on his progress in a court-ordered rehabilitation program.
His probation was also revoked in July after he was charged in a May hit-and-run traffic accident.
A Los Angeles judge reinstated it in August after Brown agreed to complete an additional 1,000 hours of community service.
Since the 2009 sentence, Brown has been involved in altercations with rapper Drake and his entourage in a New York nightclub and R&B singer Frank Ocean in a Los Angeles parking lot.