Bahraini police on Monday jailed opposition figure Zainab al-Khawaja who was convicted in 2014 for tearing up a poster of King Hamad, media and activists said.
Khawaja, a Shiite, and her toddler were taken into custody from the family home, Al-Wasat daily cited her husband as saying.
The daughter of prominent rights activist Abdulhadi al-Khawaja was sentenced to three years in prison in December 2014 after being convicted of insulting the king by ripping up a photograph of him.
An appeals court last October reduced her term to one year behind bars, while upholding a fine of 3,000 dinars (about $8,000).
Khawaja had said she would keep her son, who is reportedly just over one year old, by her side if she was jailed, Amnesty International said in October.
It was no immediately clear why authorities waited five months to take Khawaja in to serve here sentence.
"This is a terrible development," Brian Dooley of the Washington-based Human Rights First said in a statement. "Taking her back into custody only deepens Bahrain's political crisis."
Tiny but strategic Bahrain, home base of the US Navy's Fifth Fleet, remains deeply divided after authorities crushed a month-old, Shiite-led uprising that called for reforms in March 2011.