More than 900 women are standing alongside thousands of men in the December 12 municipal ballot, which will also mark the first time women are allowed to vote.
"I've been eliminated as a candidate for the municipal elections," Loujain Hathloul said in a tweet.
Saudi authorities detained Hathloul for more than two months after she tried to drive into the kingdom last December from the United Arab Emirates, in defiance of a Saudi ban on female motorists.
She had said she wanted to run "to increase the percentage of women's participation".
Another driving activist, Tamadour al-Yami, told AFP her name was also dropped from the final list of authorised candidates. She vowed to appeal, "but I don't think it will change anything."
And Nassima al-Sadah, a human rights activist and would-be candidate in the Gulf coast city of Qatif, said officials informed her late Saturday that her name had been removed.
"I don't know why," said Sadah, who was trained in electioneering by the National Democratic Institute, a Washington non-profit organisation.
Ruled by King Salman, oil-rich Saudi Arabia has no elected legislature and has faced intense Western scrutiny over its rights record.
The country's first municipal elections were held in 2005, followed by another vote in 2011. In both cases only men were allowed to participate.
From restaurants to banks, offices -- and election facilities -- the sexes are strictly segregated in the kingdom.
"We will vote for the women even though we don't know anything about them," Um Fawaz, a teacher in her 20s, said in Hafr al-Batin city.
"It's enough that they are women," she said.
The absolute monarchy, which applies a strict interpretation of Islam, has faced widespread criticism for a lack of equal rights.
Saudi Arabia is the only country in the world where women are not allowed to drive.
They must also cover themselves in black from head-to-toe in public and require permission from male family members to travel, work or marry.
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But Aljazi al-Hossaini, a candidate in Riyadh, said she did not need any man in her family to grant permission for her candidacy.
"It's by myself," the management consultant said.
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The late King Abdullah said women would participate in this year's vote. In 2013, he also named women to the appointed Shura Council, which advises the cabinet.
Abdullah died in January and was succeeded by Salman, who stuck to the election timetable.
In other Gulf states, women have had some voting rights for several years.
About 7,000 people are vying for seats on 284 municipal councils, according to the Saudi electoral commission.
Only around 131,000 women have signed up to vote, compared with more than 1.35 million men, out of a native Saudi population of almost 21 million.
Although the voting age has been lowered to 18 from 21 and the proportion of elected councillors has increased to two-thirds, winning a seat remains a challenge for women.
Hossaini said she had hoped to set up a campaign tent in Riyadh's Diriyah area. "When I asked the man to give permission for his land... he refused," she said.
Like other contenders, she plans to focus online, and has her own website, www.aalhossaini.com.
In the Red Sea city of Jeddah, Sameera Abdullah al-Shamat was also relying on Twitter, Instagram and other Internet forums widely used in the kingdom.
"My daughter and two sons are running my campaign," said Shamat, a charity worker.
Electoral democracy is still a novel concept in a country where tribal loyalties remain strong and the influence of "wasta" -- knowing the right people -- is powerful.
Saud al-Shammry, 43 of Riyadh, said it was time for a new approach.
"We strive for development and real change, free from tribal or family biases," he said, adding "there's a big possibility" he could vote for a woman, if her platform is right.