If you're copying to/from a USB drive, then that amount of CPU usage may be normal. USB (as opposed to FireWire or eSATA) uses CPU cycles to do the copying... FireWire, on the other hand, uses more of the built-in processor chips on the FireWire bus to do the copying.
In short, USB is more CPU-dependent than other external connection methods.
Also keep in mind that if your copy process is the lone process running on your system, then it'll use as much CPU as it needs or is allowed to use until some other process comes along and requests some of those CPU cycles.
Still, 60% does seem a bit high...