Loujain al-Hathloul was picked up at King Fahd International Airport in Dammam on 4 June, the human rights group Amnesty International says.
It says Ms Hathloul has been denied access to a lawyer or her family.
Ms Hathloul was arrested in 2014 when she tried to drive into Saudi Arabia from the United Arab Emirates (UAE).
Saudi Arabia is the only country in the world that forbids women from driving.
Authorities have not disclosed the reason for Ms Hathloul's latest arrest.
She is expected to be taken to Riyadh later on Tuesday, to be interrogated by prosecutors.
Amnesty International's Samah Hadid called for her immediate release, saying her "continuous harassment" was "absurd and unjustifiable".
"It appears she is being targeted once again because of her peaceful work as a human rights defender speaking out for women's rights, which are consistently trammelled in the kingdom."
While it is not technically illegal for women to drive, only men are given driving licences - and women who drive in public risk being arrested and fined by police.
Ms Hathloul was arrested in December 2014, when she tried to drive into Saudi Arabia from the neighbouring United Arab Emirates (UAE).
In November 2015, Ms Hathloul stood for election in Saudi Arabia - the first time the conservative kingdom had let women vote, or stand as candidates.
However, her name was never added to the ballot paper.
A Saudi rights activist who was detained for 73 days for flouting the country's ban on female drivers has been arrested again.