Na3 :) Ka3 would move the King to a3.
And no, I saw a game in which the commentator pointed out that a6 was a perfect place for a knight in that position. At that moment it could not do much, but sitting there it was a great threat. So depending on the position it can be good to have a knight on the rim. In most openings - I dont know 80%?- its better to have the knight on c3.
Is it justified moving Ka3 in any case? I understand knight has more power when closer to center, but are borders just a thing to avoid always?