The two women have been held for nearly a month after making their stand against the driving ban.
One of the women, Loujain al-Hathloul, 25, was detained on the Saudi side of the border with the United Arab Emirates (UAE) after trying to drive a car into Saudi Arabia on 30 November.
Her passport was confiscated and she was held at the crossing in her car overnight, according to campaign group Human Rights Watch.
She and Maysa al-Amoudi, 33, have not been charged with defying the driving ban against women, but for voicing opinions online.
A You Tube video has been published showing Loujain al-Hathloul driving a car from the UAE to the Saudi border.
Both women have been vocal Twitter supporters of a campaign opposing the ban, gathering 355,000 followers between them.
Although there is no explicit law banning women from driving, they are not issued drivers’ licences by authorities, and Saudi clerics have issued religious edicts against the practice.
Activists said their detention is the longest for any women found driving in Saudi Arabia, and that it was the first time such a case had been transferred to a terrorist court, according to the Associated Press.
The campaign group Human Rights Watch said Saudi authorities are widening a crackdown on online criticism of the government, exploiting a 2007 law against cyber crime which is being used to prosecute people for their tweets and social media comments.
De facto ban
Following the women’s detention Sarah Leah Whitson, Middle East and North Africa director for Human Rights Watch, said the Saudi government’s “degrading restrictions on women are what bring shame to the country, not the brave activists standing up for their rights”.
“After years of false promises to end its absurd restrictions on women, Saudi authorities are still arresting them just for getting behind the wheel,” she added.
The de facto driving ban came into force in Saudi Arabia in 1990, according to Human Rights Watch.
That year, 50 women were arrested for driving, and also had their passports confiscated and lost their jobs.
A woman was sentenced to 10 lashes for driving in 2011, although her sentence was overturned by the king.
In October 2013, six women were fined for driving cars in Saudi Arabia in defiance of the ban.
Defence lawyers for the two women appealed against the transfer to the specialist court, which is also used to try peaceful dissidents and activists.
An appeals court in Dammam, the capital of Saudi Arabia’s eastern province, is due to rule on the referral in the next few days.