A method for error correction deciphering of a receive apparatus in a mobile communication system includes receiving a Packet Data Convergence Protocol (PDCP) packet. The method also includes, when error correction ciphering is set, acquiring a partial Hyper Frame Number (HFN) from the PDCP packet. The method further includes comparing the partial HFN and the receive apparatus's own lower HFN of a constant bit count. The method still further includes, if the partial HFN and the receive apparatus's own lower HFN of the constant bit count are different from each other, performing an HFN correction function.