A method of allocating radio resources in a multi-carrier system is disclosed, by which a signaling message can be efficiently transmitted according to necessity of a user equipment. In a user equipment of a mobile communication system transceiving data using a plurality of subcarriers, the present invention includes the steps of if the signaling message to be transmitted is generated in the user equipment, generating a preamble sequence according to a user equipment identifier to identify the user equipment, transmitting a preamble signal including the preamble sequence and the signaling message to a base station, and receiving an acknowledgement signal for the preamble signal generated according to the user equipment identifier.