Chartchai Praditpong, senior director of the BMCL's public relations department, said the incident occurred about 7.30am at Rama 9 station.
The train was halted after the driver saw the alarm light up and passengers were offloaded and transferred to the next train.
The train in trouble was immediately moved out of service for a check.
The MRT service has returned to normal, he said.
Mr Chartchai believed the problem was with the train's alarm system. It would be repaired and then the put back in service, probably late in the afternoon.
With one tran out of operation for the tine being, only 18 were now in service, he said. Intervals between trains would be adjusted to three to four minutes.