"Her lawyer requested a delay because of the death of a close relative and the court granted the delay," Abbas Jaffari Doulatabadi said, quoted by the state news agency IRNA, without giving a date.
Reiss, 24, was arrested for having participated in demonstrations after President Mahmud Ahmadinejad's re-election in June following a disputed vote.
Accused of "collecting information and encouraging rioters," Reiss was released on bail in mid-August provided she remained in the French embassy pending her trial.
When she appeared in court in a mass trial on August 8, Iranian state media said at the time that she was accused of "collecting information and provoking rioters."
Reiss had planned to fly home after completing a six-month teaching and research assignment in the central city of Isfahan. In the closing weeks of her stay, she witnessed the protests, took pictures and emailed them to friends.
France has insisted that Reiss is not guilty and has demanded her unconditional release.
