It just indicates that your are receiving data. It depends on what program is running on the board. Can you upload new sketch to the board?
I can't upload sketch and get the following error.
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x0e
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x0e
The Rx keep lighting up on before, during, and after uploading. Is it normal?
Have you connected the corresponding serial port in Tools of Arduino IDE? Or you may switch the USB port you connect the cable?
Yes, I have connected the serial port in Tools of Arduino IDE.