Question: how long do you cook a frozen prime rib roast in the oven?
Answer: Preheat oven to 400 F. Roast the frozen prime rib in preheated oven for 1 hour 15 minutes for rare, or 1 hour 25 minutes for medium. The internal temperature should be 130 F for rare or 140 F for medium. Make sure to let the rib stand, covered with foil, for 5 minutes before slicing to let the juices redistribute.