Can I unplug the power from a computer in standby mode?

Standby mode puts your PC in a very low power state, just enough to keep the RAM and some other components active. When you unplug it, all the data in memory will be gone. You don't want to do this if you left some applications open with unsaved data. Standby mode is fine, just remember to always save your work. You don't need to unplug your PC and plug it back in after putting it into standby mode either, simply pressing a key on the keyboard or clicking the mouse should work, unless of course both are USB connected and your motherboard can't recognize them in that power state. If you have a PS/2 keyboard or mouse, pressing or clicking either should bring the machine out of standby.