The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for performing a random access procedure in a carrier aggregation with at least one SCell operating in an unlicensed spectrum, the method comprising: configuring a timer; starting the timer when the UE initiates a Random Access Preamble (RAP) transmission procedure on a first cell; stopping the RAP transmission procedure on the first cell if a Random Access Response (RAR) for the RAP transmission procedure on the first cell is not received until the timer expires.