Derakhshan, a dual Iranian-Canadian citizen, has been in jail in Iran since November 2008.
Derakhshan is reportedly facing security charges, including espionage. But his mother says in her open letter to the head of the judiciary that the family hasn't been informed of the official charges against him.
"Hossein has been in your prison for more than 500 days. And we have been waiting for him outside the prison every day," she writes.
Derakhshan's mother says that the judiciary should release Derakhshan for the New Year, as it has done in the case of a number of postelection detainees who have been allowed to go on prison leave.
"It's been eight months that you've said in all media that you have arrested those who were attempting to overthrow the establishment. On the eve of the New Year, you release all of those who had been described as the leaders of sedition. Why in your view doesn't Hossein deserve to be released?" she asked.
The International Campaign for Human Rights in Iran has said that his case is "typical of the lack of justice and due process in Iran's judiciary."