The decision, which was taken on Saturday, has been widely criticised by global rights groups, and stoked fears of an intensified crackdown on Egyptian civil society.
"We are extremely concerned by the recent decision of a Cairo Criminal Court to freeze the assets of five prominent human rights activists," UN rights office spokesman Rupert Colville told reporters.
The rights activists are Hossam Bahgat, who founded the leading Egyptian Initiative for Personal Rights NGO, Gamal Eid, Bahey el-Din Hassan, Mostafa al-Hassan and Abdel Hafez al-Tayel.
The move was linked to a long-running investigation into the foreign funding of Egyptian civil society which began in 2011 and has stoked diplomatic tensions with Washington.
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Under Egyptian law, members of rights groups operating without registration or accepting foreign funding without government permission could be jailed for life, which in Egypt amounts to 25 years.
It is not clear whether the freeze would also apply to two other NGOs partly owned by Bahgat and Eid: the Egyptian Initiative for Personal Rights (EIPR) and the Arabic Network for Human Rights Information (ANHRI), Colville said.
Bahgat and Eid are among 12 human rights who, since February, have reportedly been subjected to a travel ban linked to ongoing investigations, Colville said.
"The High Commissioner is alarmed by the continuing closure or intimidation of numerous human rights NGOs, and prosecution of their staff, by the Egyptian authorities," he added.
Such acts harmed their legitimate right to freedom of expression and of association, thereby undermining the rights of the population at large.