Quoting an unnamed informed source, the agency said that Mehdi Hashemi has been accused "of spying and of having provided sensitive information to foreigners."
Rafsanjani, who was arrested in late September, was also accused of seeking to disrupt the economy and corruption linked to oil contracts signed during his father's presidency between 1989 and 1997.
He is also accused of having undermined national security during protests that broke out after the disputed 2008 re-election of current President Mahmoud Ahmadinejad.
Mehdi Hashemi was arrested in late September upon his return to the Islamic republic from Britain, where he had lived for the past three years.
Tehran had issued an arrest warrant for him in 2010.
Just days prior to his arrest his sister, Faezeh Hashemi, was also detained and jailed for "propaganda against the regime" in line with a court decision earlier this year sentencing her to six months in jail.
Both siblings were accused by authorities of involvement in 2009 street protests that erupted after Ahmadinejad was given a second term in elections that the opposition said were marked by electoral fraud.
Faezeh Hashemi was briefly arrested with thousands of others after those demonstrations, while her brother fled the country.
Their father, an influential cleric, is seen as a moderate voice isolated by hardliners in Iran's regime.
Rafsanjani, who still heads the country's top political arbitration body, has faced demands from conservatives that he publicly condemn opposition leaders Mir Hossein Mousavi and Mehdi Karroubi, both of whom are under house arrest.