Many Egyptians have given Mohamed ElBaradei a warm welcome home
Human rights activists in Egypt say the publisher of a recent book supporting Mohamed ElBaradei has been arrested.
Mr ElBaradei, the former head of the International Atomic Energy Agency, has recently returned to Egypt and launched a campaign for political reform.
He is emerging as a potential challenger to Hosni Mubarak, who has been in power for nearly three decades.
The Arab Network for Human Rights said that Ahmed Mahanna's office was raided and his computer confiscated.
Mr Mahanna is also a blogger.
A number of other activists supporting Mr ElBaradei have been briefly detained.
Mr ElBaradei last week used his Facebook web page to issue a video message urging all Egyptians to join his newly formed group, the National Association for Change.
Mr ElBaradei has hinted he may stand against 81-year-old President Mubarak, who has ruled since 1981, in an election due in 2011. Observers believe Mr Mubarak wants his son Gamal to succeed him.
The Facebook social networking website has become a focal point for those calling on Mr ElBaradei to stand against Mr Mubarak.
The BBC's Christian Fraser, in Cairo, says there is growing momentum behind the campaign and Mr ElBaradei.
Analysts say Mr ElBaradei's appeal for many Egyptians is that he is a civilian in a country long ruled by soldiers, and that he is untainted by corruption allegations.
He has said he might stand in a presidential election if there were reforms to guarantee a fair election and if he could run as an independent candidate.
For this to happen the constitution would have to be amended.
But detractors writing in state media have portrayed him as a figure who is out of touch with Egyptian life, having lived abroad for so many years.
Mr ElBaradei, 67, built a strong reputation as head of the International Atomic Energy Agency (IAEA) and won the Nobel Peace Prize in 2005.