A method for setting ciphering activation time in a user equipment of a wireless communications system includes receiving a first RRC (radio resource control) message for activating a first ciphering key, setting an activation time of a first SRB (signaling radio bearer) as a predefined number plus a first SN (sequence number) of a last PDU (protocol data unit) of a sequence of PDUs that carry a second RRC message utilized for indicating completion of activating the first ciphering key, transmitting the second RRC message on the first SRB, prohibiting the transmission of RRC messages using the first ciphering key on the first SRB, and allowing the transmission of RRC messages on the first SRB when the successful delivery of the second RRC message has been confirmed.