if you login to hive wallet with your posting key you won't be able to reveal active key.

if you don't have hive specific keys saved somewhere or written down, log in to steemitwallet.com if you haven't changed your hive keys since steemit and just take the active key from there, if you can view it there, if you have saved the owner, active key from steemit. obviously if you just have steemit posting key it'll be the same story.