A communication device for handling a bandwidth part, BWP, comprising: at least one storage device; and at least one processing circuit, coupled to the at least one storage device, wherein the at least one storage device stores, and the at least one processing circuit is configured to execute instructions of: receiving (302; 402) a configuration for a timer, wherein the timer comprises a BWP inactivity timer; starting (304; 404) the timer in response to the configuration, when receiving a first physical downlink, DL, control channel, PDCCH, indicating at least one of a first DL assignment and a switching of the BWP; initiating (306; 406) a random access, RA, procedure and stopping the timer; restarting the timer, when obtaining that the RA procedure is successfully performed; and obtaining that the RA procedure is successfully performed, when: a) a user equipment, UE, contention resolution identity, ID, in a medium access control, MAC, control element, CE, of a first RA message received by the communication device is the same as a common control channel, CCCH, service data unit, SDU, in a second RA message transmitted by the communication device; b) the first PDCCH indicates a cell radio network temporary identifier, RNTI, C-RNTI, of the communication device and a first RA preamble for a beam failure recovery request is transmitted by the communication device in the RA procedure; or c) a second DL assignment for a third RA message is received on the first PDCCH according to a RA-RNTI of a second RA preamble and the third RA message obtained by the communication device according to the second DL assignment comprises a RA preamble identifier, RAPID, corresponding to a preamble index of the second RA preamble. at least one storage device; and at least one processing circuit, coupled to the at least one storage device, wherein the at least one storage device stores, and the at least one processing circuit is configured to execute instructions of: receiving (302; 402) a configuration for a timer, wherein the timer comprises a BWP inactivity timer; starting (304; 404) the timer in response to the configuration, when receiving a first physical downlink, DL, control channel, PDCCH, indicating at least one of a first DL assignment and a switching of the BWP; initiating (306; 406) a random access, RA, procedure and stopping the timer; restarting the timer, when obtaining that the RA procedure is successfully performed; and obtaining that the RA procedure is successfully performed, when: a) a user equipment, UE, contention resolution identity, ID, in a medium access control, MAC, control element, CE, of a first RA message received by the communication device is the same as a common control channel, CCCH, service data unit, SDU, in a second RA message transmitted by the communication device; b) the first PDCCH indicates a cell radio network temporary identifier, RNTI, C-RNTI, of the communication device and a first RA preamble for a beam failure recovery request is transmitted by the communication device in the RA procedure; or c) a second DL assignment for a third RA message is received on the first PDCCH according to a RA-RNTI of a second RA preamble and the third RA message obtained by the communication device according to the second DL assignment comprises a RA preamble identifier, RAPID, corresponding to a preamble index of the second RA preamble. receiving (302; 402) a configuration for a timer, wherein the timer comprises a BWP inactivity timer; starting (304; 404) the timer in response to the configuration, when receiving a first physical downlink, DL, control channel, PDCCH, indicating at least one of a first DL assignment and a switching of the BWP; initiating (306; 406) a random access, RA, procedure and stopping the timer; restarting the timer, when obtaining that the RA procedure is successfully performed; and obtaining that the RA procedure is successfully performed, when: a) a user equipment, UE, contention resolution identity, ID, in a medium access control, MAC, control element, CE, of a first RA message received by the communication device is the same as a common control channel, CCCH, service data unit, SDU, in a second RA message transmitted by the communication device; b) the first PDCCH indicates a cell radio network temporary identifier, RNTI, C-RNTI, of the communication device and a first RA preamble for a beam failure recovery request is transmitted by the communication device in the RA procedure; or c) a second DL assignment for a third RA message is received on the first PDCCH according to a RA-RNTI of a second RA preamble and the third RA message obtained by the communication device according to the second DL assignment comprises a RA preamble identifier, RAPID, corresponding to a preamble index of the second RA preamble. a) a user equipment, UE, contention resolution identity, ID, in a medium access control, MAC, control element, CE, of a first RA message received by the communication device is the same as a common control channel, CCCH, service data unit, SDU, in a second RA message transmitted by the communication device; b) the first PDCCH indicates a cell radio network temporary identifier, RNTI, C-RNTI, of the communication device and a first RA preamble for a beam failure recovery request is transmitted by the communication device in the RA procedure; or c) a second DL assignment for a third RA message is received on the first PDCCH according to a RA-RNTI of a second RA preamble and the third RA message obtained by the communication device according to the second DL assignment comprises a RA preamble identifier, RAPID, corresponding to a preamble index of the second RA preamble.