He was arrested in Porthacourt, the Rivers State capital, in connection with alleged possession of about N2billion.
Turnah served as Special Adviser to Dan Abia, the former managing director of the Niger Delta Development Commission (NDDC) and EFCC claims he stole the money from the commission.
The agency also said initial investigations showed that he paid the money into his personal and company bank accounts.
Some useful documents were reportedly recovered after a search conducted in his houses in Port Harcourt and Yenogoa, Bayelsa state capital.
Turnah has provided a statement and is expected to be arraigned soon.