Supporters said no traffic laws make it illegal for women to get behind the wheel but religious decrees often are interpreted as a ban against female drivers, CNN reported. One woman spent more than a week in custody in May for driving.
A Saudi woman told CNN she and her sisters were driven down Riyadh's main street by her mother Thursday and no one challenged them.
"I believe there will be women driving [Friday]," she said. "This is important for women here -- this is one of our rights."
In May, officials stopped Manal al-Sharif, 32, for driving a car. She said she was forced to sign a form pledging not to drive again and spent a week in jail.
Sharif is part of Women2Drive, an initiative demanding the right for women to drive and travel freely in Saudi Arabia. She hasn't been charged but her case remains open.
Amnesty International said Saudi Arabian leaders "must stop treating women as second-class citizens and open the kingdom's roads to women drivers."