Prominent revolutionary activist Asmaa Mahfouz was prevented from leaving the country on Tuesday.
Mahfouz was boarding a flight to Bangkok when security officials at Cairo Airport told her she was on a travel ban compiled by the prosecutor-general.
No reasons have been given by the authorities and Mahfouz has not commented on the matter.
Mahfouz was among the prominent youth figures who called for January 25 revolution.
Last year she was deported from Kuwait, where her husband works as a doctor, for unspecified reasons.
Since her return to Cairo, Mahfouz has kept a low profile compared to other activists, despite being attacked in the media by those oppose the January 25 revolution.
Mahfouz was among the recipients of the Sakharov Prize for Freedom of Thought, awarded for contributions to the so-called Arab spring.