Air Force Chief Rodzali Daud said the 'plot' was detected at 2:15 a.m. on Saturday at 200 miles northwest of the island of Penang at the northern end of the Straits of Malacca.
However, it is not known if it was the missing plane as that sort of data is not recorded by the military radar.
This would be 45 minutes after the Boeing 777-200 lost contact with air traffic control about 100 miles from Kota Baru at 1.31 a.m. on Saturday. The flight from Kuala Lumpur to Beijing had taken off at 12.41 a.m. on Saturday.
The multi-national search operations were then extended to the Straits of Malacca from the original search site in the South China Sea. The search is still on in both areas, with 42 ships and 39 aircraft from 12 countries taking part.
Rodzali said it was not confirmed that the unidentified plane was the missing flight, but Malaysia was sharing the data with international civilian and military authorities.
According to the data provided by Rodzali, a position 200 miles northwest of Penang, in the northern part of the Strait of Malacca, would put the missing plane roughly south of Thailand's tourist destination Phuket and east of the tip of Indonesia's Aceh province and Andaman and Nicobar islands.
Thailand and Indonesia have said their militaries detected no sign of any unusual aircraft in their airspace.
Malaysia has asked India for help in tracing the aircraft and New Delhi's coastguard planes have joined the search.
"We will never give up hope" of inning the plane, acting Transport minister Hishammuddin Hussein said, adding that the search will continue till authorities find the aircraft.
The flight MH370 that went missing over the South China Sea en route to Beijing from Kuala Lumpur had 227 passengers on board, including five Indians and one Indian-origin Canadian, and 12 crew members.