The five women and three men were arrested for allegedly undermining "the security and stability of the Kingdom, its social peace and national unity," the Saudi Arabian prosecutor said in a statement Saturday.
But nine other women's rights activists remain in custody because of confessions and "enough evidence against them," the statement says.
The Saudi authorities claim that the activists admitted to communicating and cooperating with "individuals and organizations hostile" to the Kingdom; recruit people able to obtain confidential information and official documents to harm the interests of the country; and provide financial and moral support to hostile elements abroad.
The detainees were not identified.
The State Security Presidency, a powerful security apparatus that reports directly to the King and the 32-year-old Crown Prince, had been monitoring the detainees before their arrest, according to the official news agency of Saudi Arabia.
Women will be able to drive on June 24
Activists were arrested weeks before Saudi Arabia lifted the ban on women's rights activism identified many of the activists as defenders of women's rights.
While the planned change has been announced around the world, the arrests a few weeks ago referred to women's rights activists and the social reform agenda of Crown Prince Mohammad bin Salman bin Abdulaziz Al Saud.
"We have returned to the starting point," the Saudi activist Sidney and author Mbad Al-Sharif had told CNN.
"We used to live in a police state, if you talk, you go to jail, and then there would be a campaign of defamation against you, saying all kinds of false things, murder of characters."
Those who are familiar with activists Detainees say they wanted more reforms. They say that the activists feared that the changes would stop if they did not continue working for greater rights.
One of the highest profile activists arrested in recent months, Loujain Al-Hathloul, was detained for 73 days in 2014 after attempting to drive from the United Arab Emirates to Saudi Arabia.
Another activist arrested, Aziza al-Yousef, 70, is one of the country's first activists for the right to drive and signed a petition in recent years calling for the end of the guardianship laws.
Tamara Qiblawi of CNN, Sarah El Sirgany and Hilary Clarke contributed to this report.