Saudi Arabia's public prosecutor has reportedly sought the death penalty for five activists, including the female rights defender Israa al-Ghomgham, reports BBC.
Human Rights Watch said they recently went on trial at a terrorism tribunal on charges including "participating in protests" in the restive Qatif region.
It has been the scene of demonstrations by the minority Shia Muslim community.
Ms Ghomgham is believed to be the first Saudi woman to possibly face the death penalty for rights-related work.
HRW warned that it set "a dangerous precedent for other women activists currently behind bars" in the Gulf kingdom.
At least 13 human rights defenders and women's rights activists have been arrested since mid-May, accused of activities deemed a risk to national security. Some have been released, but others remain detained without charge.