The officials say Wael Abbas was taken from his home in a Cairo suburb on Wednesday on accusations that include disseminating false news and joining an outlawed group. They spoke on condition of anonymity because they were not authorized to speak to media.
Egypt has arrested a number of secular activists since President Abdel-Fattah al-Sissi won re-election in March in a vote in which he faced no serious challengers.
The latest arrests come amid a wider crackdown on dissent in which thousands of people have been jailed, unauthorized protests have been banned and hundreds of websites have been blocked.
The government has said such measures are needed to restore stability and combat an insurgency in the northern Sinai Peninsula that has gained strength since 2013 and is now led by the Islamic State group.
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On Tuesday, a military court sentenced a freelance journalist who reported on the Sinai insurgency to 10 years in prison on terror-related charges. Ismail Alexandrani was convicted of spreading false news and joining an outlawed group.
International rights groups condemned the sentence and urged his release.
"Hauling a journalist before a military court not only violates his rights as a civilian but sends a chilling message to the media that independent coverage of political dissent and security threats will not be tolerated by Egypt's rulers," said Robert Mahoney, of the Committee to Protect Journalists.
Sarah Leah Whitson, of Human Rights Watch, said the verdict "exemplifies the government's vicious retaliation against journalists who report on sensitive issues."