Preheat smoker to 250°F
In a small bowl, combine garlic, salt, pepper and thyme. Coat prime rib evenly with seasoning.
Place roast, fat side up, directly on middle rack in smoker. Reduce temperature to 225°F, smoke roast for 4 to 6 hours for medium-rare to medium (1 hour per pound) or until desired temperature. (Remember, meat will continue to cook for a few minutes when taken out of the smoker and covered with aluminum foil.)
Once you have removed the prime rib, cover it with aluminum foil and let rest for 15 to 20 minutes before cutting. This will help keep the prime rib warm and juicy.