Rajab was detained earlier this month for releasing tweets deemed insulting to the government, but the public prosecution ordered his detention extended by "one week" on Saturday for participating in the January demonstration, his lawyer Mohamed al-Jishi said.
He also faces a trial, the second hearing for which is to be held on May 22, for participating in a separate demonstration three months ago in Manama.
Meanwhile, Rajab is also to face a new trial starting May 16 over his tweets, his lawyer said.
Rajab, who has led protests against the authorities since a Shiite-led uprising erupted in February last year, was arrested at the airport on May 5, as he returned from Lebanon, for "insulting a statutory body via Twitter," Mr Jishi had said earlier.
Rights groups as well the main Shia opposition formation, Al-Wefaq, have urged authorities to release Rajab, who heads the non-governmental Bahrain Centre for Human Rights (BCHR).
