Alireza Ronaghi, Al Jazeera's correspondent in Tehran, said that although there had been a request from lawyers to hold the trials as an open session, that request had not been granted.
"It seems that the judiciary has not reacted very well to that [proposal]. We haven't got any information as to how the trial has gone on, what the charges are or even who has actually being put on trial," he said.
Iran has been in political turmoil since disputed elections in June poll, when Mahmoud Ahmadeinejad, the president, was re-elected to a second term in a vote the opposition said was rigged.
The polls prompted supporters of Mir Hossein Mousavi, the leading opposition challenger, and other candidates to take to the streets.
Since then, despite government measures to curb protests, there have been intermittent opposition demonstrations, often triggering violent clashes between protesters and security forces.
In the latest round of violence during Ashoura, eight Iranians - including a nephew of Mousavi - were killed. The opposition said they died in police shooting, a charge denied by the authorities.
Baqer Moin, an Iranian journalist and author in London, said the outcome of the trials would depend on whether the defendants were public figures.
"If they are going to be part of the reformist movement - that is people who are recognised within the establishment - then things will be quite different," he told Al Jazeera.
"There are some indications that they want to put on trial some people who may be sympathetic to the opposition abroad - like the MKO [an Islamic socialist movement] or the monarchists.
"At the same time they have been arresting quite a lot of leading personalities in the past couple of weeks, some twenty leading personalities have been arrested. Their trials, we've seen in the past on television, have been partly a show trial."
Iran's domestic unrest has escalated in recent weeks, with Mousavi on Friday saying he was ready to die for his reformist campaign.
Meanwhile, Said Montazeri, the the son of the late dissident cleric Grand Ayatollah Hossein Ali Montazeri, said the government would soon have to compromise in the face of opposition protest.
"Things can't go on for long like this," Montazeri was quoted as saying in an interview with Germany's Der Spiegel magazine.
"I think the future structure of our society is not so important. It could be an Islamic Republic, a secular republic, or as far as I am concerned, even a monarchy.
"The main thing is that people can live in freedom and in prosperity," he said.