Preheat your oven to 450°F (232°C).
In a small bowl, mix together the kosher salt, black pepper, garlic powder, chopped rosemary, olive oil, Dijon mustard, and thyme to create a paste.
Place the prime rib roast on a cutting board, with the rib side down. Using your hands, rub the herb paste evenly over the entire surface of the roast, covering all sides.
Transfer the roast to a roasting pan, bone side down. Insert a meat thermometer into the thickest part of the meat, away from the bone.
Roast in the preheated oven for 30 minutes to develop a crust.
After 30 minutes, reduce the oven temperature to 325°F (163°C) and continue roasting for about 2 hours, or until the meat thermometer reads 125°F (52°C) for medium-rare.
Once done, remove the prime rib from the oven, cover it loosely with aluminum foil, and let it rest for at least 20 minutes. This allows the juices to redistribute.
Slice the roast against the grain using a sharp knife, and serve warm.