Cops found an unregistered gun in Zaire Wade‘s Burbank home after his domestic violence arrest … at least according to prosecutors.

Dwyane Wade‘s eldest son appeared in a Pasadena courtroom Thursday for his arraignment in his domestic violence case … and pled not guilty to a felony charge.

According to a reporter for LA Magazine in the courtroom … prosecutors told the judge cops found and confiscated an unregistered firearm after the alleged incident.

As you know … Zaire was arrested last month after cops showed up to a Burbank home after receiving a call about people yelling and stomping around the home, sparking fears that a domestic disturbance or someone in distress could be inside the home.

Cops say they found Zaire and a woman with lacerations all over her face … and they arrested him.

An emergency protection order was issued in court Thursday … requiring him to stay away from the alleged victim and surrender all his firearms.