In an ideal environment, your keyboard can operate up to 30 feet (10 meters) away from the USB receiver in a clear line of sight.
If you're not getting this distance, try these suggestions:
Recharge or replace the battery
Use the USB extender to change the position of the receiver
Move devices that emit radio waves or could cause radio interference away from your work area (Ex. cell phones, radios, wireless routers, microwaves)
To determine if your environment is shortening your operating range, try using your keyboard somewhere else to see if the distance improves. If it does, look for other possible sources of interference you can remove from your work area.