The assorted girl, an educational who had been lecturing at an Australian college, has been given a 10-year sentence.
British-Iranian national Nazanin Zaghari-Ratcliffe is also imprisoned there after being convicted in 2016 of conspiring to topple the Iranian leadership.
The arrests consist of two female British-Australian nationals and the Australian boyfriend of one.
The women and the man are incarcerated in the Evin jail in Tehran where 41-year-old Nazanin Zaghari-Ratcliffe, a British-Iranian mother of one, has been held on spying charges since 2016.
"The Department of Foreign Affairs and Trade is providing consular assistance to the families of three Australians detained in Iran", a spokesperson told AFP, declining to comment further citing privacy obligations.
The detention of two dual British-Australian citizens, if confirmed, would deepen tensions between London and Tehran and pose a further challenge to embattled Prime Minister Boris Johnson.
Though the charges against the second woman remain unclear, Iran routinely hands out 10-year terms for spying charges, the Times said.
The Australian government's official travel advice for Iran overall is for people to reconsider the need to travel to Iran "due to the risk that foreigners, including Australians, could be arbitrarily detained or arrested".
"The foreign secretary met the Iranian ambassador this morning and raised serious concerns about the number of dual national citizens detained by Iran and their conditions of detention", the British foreign ministry said in a statement.
"Iran doesn't recognise dual nationality", DFAT warns on its website.
The latest arrests are also raising questions over the safety of travellers from other nationalities.
Last month, Australia's Prime Minister Scott Morrison announced the country's defense force would work alongside the U.S. and the United Kingdom on a maritime security mission in the Strait of Hormuz.
The family of the blogger and her partner say their arrest is a misunderstanding and they were unaware that flying a drone in Iran requires a permit. Oil prices jumped as investors feared that attacks on oil tankers risked a disruption of shipments in the Strait of Hormuz, which passes by Iran and is the most important place on the planet to the global supply of oil.