Egyptian police arrested a publisher in a dawn raid on his house on Saturday and confiscated copies of a book supporting former UN nuclear watchdog chief Mohamed ElBaradei, a human rights group said.
Police also seized a computer belonging to Ahmed Mahanna, who runs the Dawin publishing house, the Arabic Network for Human Rights Information said in a statement.
Gamal Eid, the director of the rights group, told AFP that Mahanna was being held in a state security prison but had not been charged.
"He had published a book on ElBaradei more than week ago. Police seized copies of the book and his computer," Eid said.
Police did not immediately comment on the group's statement.
ElBaradei has emerged as Egypt's highest-profile dissident since he retired as head of the International Atomic Energy Agency at the end of last year.
He has said he would run for president if Egypt's constitution were amended, a condition ruled out by President Hosni Mubarak who has been in power ever since 1981.