Ali Belhadj, the former number two in the banned Islamic Salvation Front (FIS), was arrested on 27 July after an Aljazeera television interview where he supported the resistance to the US-led forces in Iraq.
"An investigating judge questioned Ali Belhadj and ordered him back to prison," Abdelkader Moghni, a former FIS leader, said.
Belhadj's son Abdelfattah added: "The authorities has returned my father back to jail to complete the questioning."
Algeria's General Prosecutor Kaddour Beradja said Belhadj faced charges of "praising acts of terrorism, inciting murder and distributing subversive leaflets".
Belhadj told Aljazeera in a telephone interview: "I congratulate the mujahidin fighting in Iraq and ask God to help them in the face of occupiers and their allies, especially that the sharia says that allies of occupiers face the same fate as occupiers themselves."
Belhadj also expressed his opinion regarding the killing of two Algerian diplomats in Iraq, for which, according to a website, al-Qaida had claimed responsibility.
Al-Qaida regards Algeria's government as infidel and said in a web-statement: "We won't forget what Algeria did to Muslims, by killings, destruction and spilling their blood."
While the Algerian government has said it supports Iraq's sovereignty, it has not voiced opposition to US policy there.
FIS had won Algeria's first multi-party legislative elections in December 1991 by overwhelming majority. But the army scrapped the polls and cracked down on the party, banning FIS and other organisations. The army crackdown and subsequent violence led to the death of 150,000-200,000 people.
"We won't forget what Algeria did to Muslims, by killings, destruction and spilling their blood"
Belhadj was released from a military prison in 2003 after serving a 12-year-term for what the Algerian government called "threatening national security".
"Belhadj has been sent back to jail, but we do not know when the judge will summon him for further questioning," his brother, Habib Belhadj, who is also his lawyer, said.