Online court records say Dennard's lawyer filed a written arraignment and the plea on Tuesday. A trial date has not been set.
Dennard remains free on bond. He faces up to five years in prison if convicted on the third-degree assault charge.
Dennard is accused of striking an officer during a disturbance on April 21, five days before the NFL draft began. He was the 2011 Big Ten defensive back of the year and had been projected to be a second- or third-round pick before his arrest.
The Patriots took Dennard in the seventh round (224th overall) and signed him to a four-year contract on Tuesday.
Information from The Associated Press was used in this report.