Add the Dijon mustard, olive oil, vinegar, and lemon juice to the bowl with the seasonings and mix well. Place the rib roast on a rack inside of a roasting pan.
Cover the rib roast with the mustard mixture. Place the rib roast in the oven for 15 minutes. Reduce heat to 325 degrees and continue cooking for 1 hour 59 minutes (for medium-rare roast).