Alaa Abdel Fattah's arrest came two days after Egyptian authorities stifled calls for fresh protests against President Abdel Fattah el Sisi's rule, deploying security forces and closing many of Cairo's main thoroughfares.
A leading Egyptian pro-democracy activist was re-arrested on Sunday while he was under probation, his family and a security official said.
The arrest of Alaa Abdel Fattah came amid a sweeping security clampdown following small but rare anti-government protests earlier this month.
Abdel Fattah rose to prominence with the 2011 pro-democracy uprisings that swept the Middle East and in Egypt, toppled long-time President Hosni Mubarak.
To many, his imprisonment three years later — at a time when authorities imposed draconian laws banning public gatherings and unauthorised demonstrations — was another sign of Egypt's return to autocratic rule.
His release in March came after five years in prison for taking part in a peaceful protest against military trials for civilians.
His mother, Laila Soueif, told The Associated Press that Abdel Fattah was arrested on Sunday from the police station in the Dokki area of Cairo.
"I was waiting for him to walk out this morning, but the area around the police station was sealed off. They did not allow me to get in as they were doing every day," she said.
Under the terms of his release, authorities required Abdel Fattah to report to a police station and spend every night there for the next five years.
Soueif, who is a university professor, said she has been going to collect him every morning in the past days, for fear he could be re-arrested after a wave of arrests targeting anti-government protesters.
A spokesman for Egypt's Interior Ministry did not immediately respond to requests for comment.
A security official says Abdel Fattah was taken to prosecutors for an investigation into claims he has called for protests. The official spoke on condition of anonymity because they were not authorized to brief media.
Abdel Fattah has been detained several times before under different governments for lobbying for civil rights on social media and in public.
An influential blogger, he hails from a family of political activists, lawyers and writers. His late father was one of Egypt's most tireless rights lawyers, his sisters are also political activists and his aunt is the award-winning novelist Ahdaf Soueif.
Sunday's arrest came two days after Egyptian authorities stifled calls for fresh protests against President Abdel Fatah el Sisi's rule, deploying security forces and closing many of Cairo's main thoroughfares.
Scattered protests had erupted on September 20 after corruption allegations by an Egyptian businessman living in self-imposed exile against the president and the military. The allegations were dismissed by el Sisi as "sheer lies."
More than 2,000 people were arrested in the days after, according to right lawyers. The country's general prosecutor said his office had questioned no more than 1,000 people over the protests.