On Monitoring Control Panel, CPU utilization of Virtual Server Instance sometimes exceed 100%. Is this normal?

Yes. The maximum value is “100 percent x number of CPU cores”. (Example: If the virtual server instance is 16 CPUs, the value ranges from 0 to 1600 percent.)
So CPU Utilization may exceed 100%, depending on the flavor of the virtual server.

Reference:
Service Description - Monitoring - Data Collection/Accumulation - Virtual Server Instance

Service Description - Virtual Server - Plan List