"We call on Egyptian authorities to immediately release all individuals who have been detained in relation to their work as human rights defenders," Ravina Shamdasani said in a statement.
"Intimidation of political opponents, activists and human rights defenders for peaceful exercise of their fundamental rights to freedom of expression and association must be halted."
The U.N. rights commission said dozens of plainclothes policemen stormed the offices of the Egyptian Center for Economic and Social Rights Wednesday. Some employees were arrested and allegedly beaten.
Shamdasani said the whereabouts of Mohamed Adel Fahmi, a member of the revolutionary April 6th Movement, were unknown. He was one of six people arrested. The other five were released after less than a day in custody.
The spokeswoman called for an independent investigation into the raid.
Her comments came after former U.N. Secretary-General Kofi Annan, chairman of peace advocacy group The Elders, praised Egyptian leaders for pro-democratic revisions to a proposed constitution.
The first post-revolution constitution was deemed pro-Islamic. Egyptians are to vote on the new version next month.