The Argentina captain was labelled â€˜selfishâ€™ by Anfield boss Roy Hodgson, who claimed the midfielder had refused to play for the club in a Europa League tie to try to force through his move.
But Mascherano, 26, said: "Roy Hodgson knows the truth. This is a happy moment for me so now is not the moment to say it, but a lot of lies have been spoken about me and shortly I will respond."
The midfielder said he was close to moving to Barca a year ago but Liverpool refused to sell him because Xabi Alonso was leaving.
He added: "When the best club in the world calls you, then it is something that you want to happen."