The youngest brother of former Algerian President Abdelaziz Bouteflika and two former intelligence chiefs were on Sunday placed in custody, state TV reported.
Said Bouteflika and the two generals, Athmane Tartag and Mohamed Mediene, were arrested on Saturday, it said.
The three are under investigation over "harming the army's authority and plotting against state authority," it said, quoting a statement from the prosecutor at the military court of Blida, south of Algiers.
Said Bouteflika, who served as a top advisor to the presidency, acted as Algeria's de facto ruler after his brother suffered a stroke in 2013 that left him in a wheelchair.
Mediene had been intelligence chief for 25 years until his dismissal by Bouteflika in 2015.
Massive protests calling for a radical change to Bouteflika's government pushed the ailing president to resign on April 2. Demonstrators continue to demand the removal of all those linked to the former administration.
Army chief of staff Ahmed Gaed Salah has promised to rid the country of corrupt politicians and military officials in order to restore confidence among the people.