Preheat the oven to 500F. In a mixing bowl, combine butter, garlic, rosemary, thyme and Montreal steak spice and salt. Give a good mix with a fork.
Spread the garlic butter mixture over top of the prime rib and the sides. Place it on a roasting rack.
Roast for 15 minutes, reduce the heat to 325F and roast 45-50 minutes for medium doneness (inner temperature should be around 135-140F for medium doneness). Transfer to a cutting board, slightly cover with foil and let rest for 20-30 minutes. Slice and enjoy!