The writer and broadcaster will be joined by international landscape guru Martha Schwartz.
The panel will be completed by Ian Ritchie, architect and academic Peter Cook and AJ editor Isabel Allen.
Following in the footsteps of previous celebrity judges such as artist Tracy Emin and author Julian Barnes, Frostrup will help decide the winner of the most important prize in British Architecture.
The shortlist for the prize, which will be picked from the 2006 RIBA award winners, will be revealed in August.
The awards ceremony itself will take place in October at the Roundhouse in Camden, recently refurbished by John McAslan.