Chaab, with both Swedish and Iranian citizenship, has been sentenced to death for alleged terrorist crimes.
He is accused, according to the court documents, of acting as a leader of the separatist group ASMLA, which is labeled a terrorist by Iran.
The court also accuses him of planning and carrying out bombings in Khuzestan, an Iranian province bordering Iraq, in 2018. Many of the victims belonged to Iran's Revolutionary Guard.
ASMLA wants to see an independent state in the province.
The Swedish Foreign Ministry has previously said that it is in contact with representatives of Iran in the case, and that it has unsuccessfully requested consular access.
Described as a political activist
Chaab disappeared in Turkey in October 2020. The Turkish government accuses Iran of kidnapping Chaab from the country, and Turkey's intelligence service has released surveillance footage that it says shows the kidnapping.
Chaab has been described as a political activist who lived in exile in Sweden for several years.
After his arrest, he was shown on Iranian television, and then confessed to the deadly crime.
However, the outside world usually does not trust such confessions, as they are often feared to have been made after torture.
Another Swedish-Iranian is imprisoned in Iran in a similar situation.
It is about the doctor and researcher Ahmadreza Djalali, who was arrested in 2016 when he visited the former homeland.
He is accused of collaboration with the Israeli spy service, and is also sentenced to death.
His execution date has been postponed several times.