Mobile satellite communication method and system capable of carrying out carrier activation with reliability of a communication path secured

In a mobile satellite communications system comprising an earth station (10), a mobile station (20) with a mobile antenna (24), and a communications satellite (30) for mediating communications between the earth station and the mobile station, the earth station comprises a carrier frequency variation detecting device (18) for detecting a received carrier frequency due to a doppler effect to produce a frequency variation detected signal. Although an earth signal processing circuit (12) transmits a burst carrier signal or a maintaining burst signal to the mobile station when an information signal such as a speech signal to be transmitted is not supplied thereto, the earth signal processing circuit extends a burst transmission duration for the maintaining burst signal in response to the frequency variation detected signal and it results in making the mobile station easily carry out antenna tracking control. In addition, the earth signal processing circuit continuously transmits the carrier signal when a received frame synchronization is pulled out.