AN MD90 ON SECOND START OF DAY HAD L AND R ENG SYS FAIL MESSAGES ON OVERHEAD ANNUNCIATOR PANELS. FOUND EMER THRUST REVERSER HAD BEEN ACTIVATED ON LNDG. INSPECTION REQUIRED.

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NORMAL SCHEDULED LNDG AT ZZZ RWY 19; WELL WITHIN TOUCHDOWN ZONE; FLAPS 40 DEGS; MEDIUM AUTOBRAKES. NORMAL APCH; FLARE; AND TOUCHDOWN. AFTER MAIN LNDG GEAR TOUCHED DOWN; I LOWERED NOSE TO RWY SURFACE AND THEN APPLIED REVERSE THRUST AS PER SOP. THE MEDIUM AUTOBRAKES WERE NOT VERY EFFECTIVE SO AT SOME POINT IN THE ROLLOUT; I APPLIED LIGHT MANUAL BRAKING. AT THE APPROPRIATE TIME AND AIRSPD; I STOWED THE THRUST REVERSERS. WE WERE NEARLY AT TAXI SPD PASSING TXWY E; BUT I CONTINUED PAST TXWY E AND TURNED OFF AT TXWY W INSTEAD. NO ABNORMAL INDICATIONS WERE DETECTED BY EITHER FLT CREW MEMBERS AT ANY TIME DURING THE LNDG; ROLLOUT; OR TAXI IN. ON THE NEXT FLT; ZZZ TO ZZZ2; NO STATUS MESSAGES OR ABNORMALITIES WERE DETECTED PRIOR TO BEGINNING ENG START. DURING START OF L ENG; L AND R ENG SYS FAIL MESSAGES WERE ILLUMINATED ON THE OVERHEAD ANNUNCIATOR PANEL. I ASKED THE TUG DRIVER TO REMAIN CONNECTED. WE IMMEDIATELY CONTACTED THE DISPATCHER AND THE ZZZ MAINT COORDINATOR AND INFORMED HIM OF THE INDICATIONS. HE INFORMED US THAT THESE MESSAGES COULD ONLY BE CLRED BY MAINT AND THAT WE WOULD HAVE TO RETURN TO THE GATE. WE THEN SHUT DOWN THE ENG AND ASKED TO BE TOWED BACK TO THE GATE. ONCE AT THE GATE; A CONTRACT MAINT PERSON CLRED THE FAULTS AND REQUESTED THE FLT CREW RUN BOTH ENGS. AS DIRECTED BY MAINT; WE STARTED THE L ENG AND ALL INDICATIONS APPEARED NORMAL. WE THEN SHUT DOWN THE L ENG AND STARTED THE R ENG. ALL R ENG INDICATIONS WERE ALSO NORMAL. WE WERE THEN INSTRUCTED BY THE ZZZ MAINT COORDINATOR TO SHUT THE ENGS DOWN; SO WE DID SO. FURTHER INVESTIGATION BY THE ZZZ MAINT COORDINATOR APPARENTLY REVEALED THAT THE EMER REVERSE THRUST HAD BEEN ACTIVATED ON LNDG ROLLOUT AND THAT AN INSPECTION WOULD BE NECESSARY. THRUST REVERSER OP DID NOT SEEM UNUSUAL OR ABNORMAL. I DID NOT FEEL THE INCREASE OF RESISTANCE (17 LBS REQUIRED) ON THE REVERSER LEVERS REQUIRED TO ATTAIN ACTIVATION OF THE EMER REVERSE THRUST; NOR WAS I AWARE THAT IT HAD OCCURRED UNTIL I WAS INFORMED BY THE ZZZ MAINT COORDINATOR. I DID NOT DELIBERATELY OR INTENTIONALLY ACTUATE THE EMER REVERSE THRUST.