The X-Arcade™ comes with both USB and PS/2 connection options, it is recommended to use the USB connection if you have a wireless or USB keyboard. Connected this way you do not need to have a keyboard plugged into the X-Arcade™ to use it.
NOTE: The X-Arcade™ will not work in a PS/2 keyboard port unless a keyboard is plugged into the back of the X-Arcade™ when the computer boots up.
If you have a USB or wireless keyboard you may be able to use a standard USB to PS/2 adapter to plug your keyboard into the back of the X-Arcade™, many USB keyboards even come with this adapter. This may work, but the only way to find out for sure is to try it with your hardware. If the USB to PS/2 adapter does not work for you (or if you have a wireless keyboard/mouse combo with a single USB receiver for both), you will need to plug the X-Arcade™ into a USB port instead.