The present invention relates to a wireless communication system and, more particularly, to a method and an apparatus for transmitting and receiving a frame supporting a short MAC header in a wireless LAN system. A method for receiving a frame by a station (STA) in a wireless communication system in accordance with one embodiment of the present invention may comprise the steps of: receiving the frame including a sequence control (SC) field; determining a packet number (PN) using the value of the SC field and a partial PN value stored in the STA; and performing decryption for the frame using the PN. When the decryption is performed after reordering a block ACK for the frame, an operation can be performed to increase the partial PN value stored in the STA by 1 if the sequence number value of the SC field of the received frame is less than the previous sequence number value.