can you untap something that is already untapped

[Brawl]

can you untap a card that is already untapped?

[seba1983]

you can not untap an already untaped permanent if untaping is used to pay any activation cost. appart from that you should be able to target an untaped permanent with an effect that would untap it. im not 100% certain because i could not find a confirmation on that in the comp rules just now. someone confirm plz.

[Twanos]

confirmed. Unless the spell or ability in question states it only works on a tapped permanent you can target an untapped perm with an untap effect it will simply not have a result.