Loujain Hathloul has been detained since December 1 after she tried to drive into the kingdom from neighbouring United Arab Emirates in defiance of a ban.According to other activists, it seems the authorities "are intent to basically make an example of the two women."
Saudi Arabia is the only country in the world which does not allow women to drive.
Maysaa Alamoudi, a UAE-based Saudi journalist, arrived at the border to support Ms Hathloul and was also arrested.
Activists said the ruling came at a hearing in Al-Ahsa, in the kingdom's Eastern Province.
They did not provide full details of the allegations against the pair but said investigations appeared to focus on the women's social media activities rather than their driving.
"They will transfer her case to the terrorism court," said an activist familiar with Ms Hathloul's case, adding that her lawyer plans to appeal.
Because an empowered Muslim woman is obviously a threat.
Hard to believe that in the 21st century there are women who are not allowed to drive.
More on Hathloul and Alamoudi.