Preheat. Fire up the smoker and allow it to preheat to 225 degrees F while you prepare the prime rib.
Trim the meat. Trim any excess fat from the top of the roast down to 1/4 inch thick.
Season. In a small bowl combine the mustard, Worcestershire sauce, and garlic. Slather the entire roast with the mustard mixture and season liberally with salt and pepper.
Smoke. Place the roast on the grill and close the lid. Smoke until the internal temperature of the roast reaches 120 degrees F for Rare or 130 degrees F for Medium. For a rare, bone-in roast, plan on 35 minutes per pound of prime rib.
Rest. Remove the roast to a cutting board, cover the roast with foil, and allow it to rest for 20 minutes.
Increase temp in smoker. While the roast is resting, increase the temperature of your grill to 400 degrees F.
Sear. Once the grill is up to temperature, return the roast to the grill and sear until you reach your desired internal temperature. Pull the roast off at 130 degrees F for rare, 135 degrees F for medium rare, or 140 degrees for medium. This process should go quickly, so keep an eye on your temperature.
Rest, slice, and serve. Remove your roast to the cutting board and let the meat rest for at least 15 minutes before slicing and serving.