Yes.
Line voltage: 100-120V AC or 200-240V AC (wide-range power supply input voltage)
Frequency: 50Hz to 60Hz single phase
The same spec is given on the UK and US versions of the tech spec pages. You may want to specifically check out the Apple site for the country where you intend to buy just to be sure, because sometimes models do vary.
[edit: oops, the above is for the new Intel machines... let me double check...]
Okay, yes, that was the same for the G5 towers:
http://www.apple.com/powermac/specs.html