The men were detained around 4 am on Thursday morning in Killygordon, east Donegal.
A Garda spokesman said: “A file will be prepared for the Director of Public Prosecutions.” .
The men were arrested after a lethal booby trap bomb was found under the car of a couple who are both serving PSNI officers.
The device was found outside their Glenrandel home in the village of Eglinton.
A man arrested in Eglinton under section 41 of the Terrorism Act remains in custody at the serious crime suite in Antrim.