The workers had been taken hostage Friday from the Dadaab Ifo II camp in an attack on two vehicles belonging to the NRC. Abdi Ali, a driver for the relief organization, was killed and two other local local employees were injured.
The four hostages had been held in Somalia, the Kenya Broadcasting Corp. said Monday.
They were rescued in a combined operation by the Kenya Defense Force and Somali Transitional Federal Government troops about 19 miles north of Dhobley, the news agency reported.
The aid workers, who are from the Philippines, Norway, Pakistan and Canada, were unharmed.
"We are thankful to know that our four colleagues have been found and safely returned to Kenya. This is a day of relief for us and for the families of the abducted," Elisabeth Rasmusson, secretary-general of the Norwegian Refugee Council, said Monday in a statement.
Two Spanish women working for Medicines Sans Frontiers were kidnapped at the Dadaab refugee camp in October, the KBC said. They have not been found.