CRJ200 flight crew experiences a R REVERSER UNLOCKED amber caution message climbing through 12000 FT. QRH procedures were complied with; an emergency declared; and the flight returned to their departure airport.

Narrative

During climbout; before thrust reduction in the after takeoff check; the pilot flying and I noticed the amber 'REV' being intermittently displayed on the right engine N1 gauge. At that time there was not an associated CAS message. We completed the after takeoff checklist and the pilot flying transferred the aircraft controls and radios to me. The Captain then radioed company to discuss the situation with maintenance. While on frequency with company and climbing through approximately 12;000 FT; we received a 'R REVERSER UNLOCKED' amber caution message. The Captain told company of the new message and that we are returning. I then transferred the controls back to the Captain and he instructed me to declare an emergency with Center and to advise that we are returning to ZZZ. The Captain then instructed me to complete the QRH checklist for 'R REVERSER UNLOCKED' amber caution message and he took control of the radios. After completing the QRH procedure; we had operational use of the right engine. I then notified the Flight Attendant of the situation and that we were returning and to secure the cabin. The Captain then transferred the aircraft controls and radios to me and he made a PA announcement to advise the passengers of the situation. I then transferred the aircraft controls back to the Captain. We proceeded to make a visual approach to Runway 6L and emergency equipment was standing by. We landed at approximately 49;000 LBS at less than 300 FPM descent rate. After completing the After Landing Checklist; I transferred the radios to the Captain and I notified ops that we were returning to the gate. Maintenance met us at the gate.