I think an anti hero could have good intentions and heroic qualities but they can also be flawed and may have some flaws and qualities that the villains posses.They may not go about enforcing or carrying out justice by the book for example they may become a vigilante.To me Anti Heroes or Antiheroines would be characters like
The Punisher http://www.comicvine.com/punisher/4005-1525/
Faith from Buffy The Vampire Slayer http://www.comicvine.com/faith/4005-42342/
Anya from Buffy the vampire slayer
http://www.comicvine.com/anya/4005-20100/
Angel from Buffy the Vampire slayer http://www.comicvine.com/angel/4005-20094/
Spawn http://www.comicvine.com/spawn/4005-3381/
Vampirella http://www.comicvine.com/vampirella/4005-1677/
The Huntress http://www.comicvine.com/helena-wayne/4005-45563/
Pantha http://www.comicvine.com/pantha/4005-32362/
Lady Death http://www.comicvine.com/lady-death/4005-1847/
Magneto http://www.comicvine.com/magneto/4005-1441/
Catwoman http://www.comicvine.com/catwoman/4005-1698/
Poison Ivy http://www.comicvine.com/poison-ivy/4005-1697/
To me an unwilling hero would probably not want to be bothered saving the world but would probably be forced into doing it by circumstances .They may become a hero by accident and may not have intended to be a hero.Perhaps they could be a bad guy or girl who redeemed themselves.
Obviously all of the characters I mentioned where fictional and had supper powers or special abilities.I don't expect to be able to do what they do but there could be ordinary things I could do to help make things better in this world instead of being destructive.A lot of the characters I mentioned had potential to both good and bad and aren't easily defined.Some are more destructive than others but even though some of like them Poison Ivy or Magneto are villains they occasionally do good and do have some good intentions.
I think these characters could be described as unwilling heroes although I could be wrong
Squall Leonhart http://finalfantasy.wikia.com/wiki/Squall_Leonhart
Prince of Persia http://princeofpersia.wikia.com/wiki/Sands_of_Time
http://princeofpersia.wikia.com/wiki/Prince_(Sands_of_Time)
The prince from the from the game series not the movie which Disney ripped off.Don't get me wrong Jake Gyllenhaal is cute but Disney don't do the game character justice
Yuri Hyuga http://shadowhearts.wikia.com/wiki/Yuri_Hyuga
Raziel http://legacyofkain.wikia.com/wiki/Raziel