The use of canned air is safe. Just be sure that the machine is shut down. Also to unplug the power source. Just be sure to read the directions on the can.
Canned air works just fine (so long as you pay attention to the directions and hold the can upright so you don't end up spraying liquid into your Mac). If it's very dusty, I'd recommend carrying it outside to blow off and save yourself having to vaccum (or a case of blacklung).