United meet the Catalan club for the second time in nine weeks when they play the final match of their pre-season tour of the United States at the weekend.
Barcelona beat United 3-1 in the Champions League final in May and Ferguson feels that his side must raise their game to match the La Liga champions.
"Barcelona's feats over the last two or three years have elevated them in everyone's mind. Currently they are the best team in the world," said Ferguson.
"I'm quite happy to be in second place at this moment in time. Our challenge is to get to that level."
Barcelona's Lionel Messi, who was instrumental in the Champions League win over United, will miss Saturday's match after taking part in the Copa America. Meanwhile, United's Javier Hernandez has been ruled out with concussion.