A man was found unresponsive on an MBTA bus Friday morning and was later pronounced dead, the MBTA said. The 67-year-old man was on a Route 68 bus when the bus operator found him still onboard at Kendall Square, said MBTA spokesman Joe Pesaturo. The operator reported the situation at 6:56 a.m., Pesaturo said. The man, who has not been identified, was brought to Massachusetts General Hospital, where he was pronounced dead, said Pesaturo. The operator of the bus recalled the man boarding the bus about 15 minutes before its arrival at Kendall Square, he said. “The death is not considered suspicious,” Pesaturo said.