It will prevent light aircraft flying over the area below 10,000 ft (3,048 m) between the 3-5 September.
The Civil Aviation Authority (CAA) imposed the restriction following a request from police.
The ban will not affect emergency services, or commercial flights travelling to and from Cardiff and Bristol airports.
In an advisory sent out to pilots, the CAA said the restriction was part of the security operation being put in place to protect heads of state, including President Barack Obama, who are attending.
Unauthorised aircraft will not be able to fly over the area from Newport, Cardiff and the Gwent valleys, to Ross-On-Wye, Bristol and Minehead.
Flights which breach the ban will be intercepted by police air support.
A no-fly zone has been put in place for parts of south Wales and Bristol during the three-days of the Nato summit.