Mohammad Hashemi and Bahareh Hedayat were arrested and sent to the notorious Tehran prison of Evin on Sunday, the Etemad newspaper said.
The two are members of the central council of the pro-reform student group The Office to Consolidate Unity.
Their detention raised the number of students arrested throughout the country to around 18 since the anniversary of student protests on July 9, 1999, the Kargozaran newspaper said.
An unnamed judiciary source told the state news agency IRNA that the two had been arrested accused of "links with illegal and counter-revolutionary groups outside Iran."
"Their arrest is not related to their student activities," the source said.
The other arrests have been made in the northeastern city of Mashhad, the southeastern Sistan-Baluchestan province and the province of Tehran.
Groups of students hold small gatherings annually to commemorate July 9, which marks the most significant clash between the authorities and students in the Islamic republic.
The riots were sparked when hardline vigilantes stormed student dormitories and the ensuing violence left dozens of students wounded and many arrested.
Hashemi, Hedayat and some other members of their group were also arrested in July 2007 for holding a sit-in protest against the imprisonment of three colleagues from Tehran's Amir Kabir university, a hotbed of student activism.
President Mahmoud Ahmadinejad was famously heckled during a 2006 speech at the prestigious university.
