A Supreme Court judge has banned the wife of an accused terrorist from wearing a niqab veil in the court's public gallery.

The woman, who is married to a man accused of plotting a Christmas Day terrorist attack at Melbourne landmarks, had her application to wear the garment dismissed in court.

A woman in a niqab.

Justice Christopher Beale ruled Supreme Court spectators must have their faces uncovered in order to prevent misbehaviour in the courtroom that could lead to the discharging of a jury.

A niqab is a traditional Muslim garb that covers the head and face except for an opening for the eyes.