Tabbou "was arrested in Dely Ibrahim," a suburb of the capital Algiers, "by plainclothes police," his brother Djaffar said in a Facebook post late Tuesday, citing lawyer Toufik Belala.
The brother added that Tabbou had not been informed of when he would appear before prosecutors or the charges he might face.
Tabbou's lawyer Belala was unavailable for comment.
Tabbou, 48, was one of the most recognisable faces during mass rallies, led by the Hirak pro-democracy movement, that began in February 2019.
Tabbou leads a small, unregistered opposition party, the Democratic and Social Union (UDS).
The protests demanded a sweeping overhaul of the ruling system in place since the North African country's independence from France in 1962.
He was sentenced in March 2020 to one year in jail for "undermining national security" over his criticism of the army's involvement in politics.
After his release from prison, he was detained again in April 2022 for 24 hours for unknown reasons.
The Hirak protests had forced longtime president Abdelaziz Bouteflika to step down. Demonstrations continued in a push for deep reforms but the movement waned when the coronavirus pandemic struck.
Dozens are still detained in Algeria over links to Hirak or human rights activism, according to the National Committee for the Release of Detainees.
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