ASPEN, Colo. -- Actor Charlie Sheen has pleaded not guilty in Colorado to domestic violence charges stemming from a Christmas Day incident with his wife.

Sheen entered his plea Monday to counts of menacing, criminal mischief and assault. A trial is scheduled July 21.

The star of "Two and a Half Men" on CBS is accused of putting a knife to the throat of Brooke Mueller Sheen while they vacationed in Aspen.

The maximum penalty for the most serious charge of menacing is one to three years in prison.

Sheen voluntarily entered a rehab facility last month. His publicist, Stan Rosenfield, called it "a preventive measure" but didn't say why Sheen sought treatment.

According to the executive producer of "Two and a Half Men", Sheen will return to the set this week and continue his treatment at night, when filming is complete.

Mueller, too, spent time at a rehab center last month, but she left The Canyon in Malibu due to a privacy breach.

Sheen and Mueller, the actor's third wife, married in 2008 and have twin sons.

The couple say they want to reconcile.

Sheen's trial is expected to begin on July 21.

The case could end with a plea deal in which Sheen serves a minimal amount of jail time.