The country's interior minister has toughened the Saudi government line on the women drivers' campaign, saying anyone breaking the law is likely to face unspecified punishment.
Badawi Al Rasheed, a Saudi academic and expert on women's rights doesn't think many women will flout the ban, because of worries of their safety.
"We have heard there are counter campaigns to actually drive the women away from the streets, either by harming them or by crashing their cars," she said.
However, a Saudi woman said she got behind the wheel Saturday and drove to the grocery store without being stopped or harassed by police.
Despite warnings by police and ultraconservatives in the kingdom against defying the ban, at least four women have successfully driven, May Al Sawyan said.
Though no specific Saudi law bans women from driving, women are not issued licences.
Powerful clerics who hold far-reaching influence over the kingdom's ruling monarchy enforce the ban. Clerics warn that "licentiousness" will spread if women drive.
In the runup to the campaign, police warned that anyone disturbing public order would be dealt with forcefully.
Ultraconservative clerics also protested earlier in the week against the online petition campaign, which was launched in late September and says it has more than 16,000 signatures.
The account's website, oct26driving.org, and official English language YouTube account were hacked on Friday, according to activists.
Activists posted a four minute-long video on the campaign's official Arabic account that they said depicted Al Sawyan driving in Riyadh.
She wore sunglasses and her hair was covered by the traditional black headscarf worn by Saudi women, but her face was otherwise visible.
Like other female drivers defying the ban in Saudi Arabia, Al Sawyan said she has obtained a driver's licence from abroad.
"I am very happy and proud that there was no reaction against me," she told The Associated Press by telephone. "There were some cars that drove by. They were surprised, but it was just a glance. It is fine ... They are not used to seeing women driving here."
The activists behind the campaign have said they believe the public mood is changing, with many more people - including an increasing number of men - publicly supporting the lifting of the ban.
Saudi Arabia is the only country in the world that doesn't issue drivers' licences to women.