The Gunners host Luis Enrique's side on Tuesday in the first leg of their last-16 clash as they look to reach the quarter-finals of the competition for the first time since 2010.
But Herrera believes Barca still have the edge despite Arsene Wenger's side's improvements in domestic football.
"I think it’s going to be harder for Barcelona this year," he told Marca. "I think that Arsenal, aside from having some outstanding players, are brimming with self-confidence this season, both in the Premier League and the Champions League.
"That said, I think Barca are better. Not much better, but still better. It’s going to be a great tie.
"If Leo Messi has his day, there’s little you can do. Of course, your job as the opposition is to ensure that he doesn’t have his day, but if he is 100 per cent on form and has his day, you can either pray or forget about it."
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But when comparing Ozil and his opposite number for Barcelona, Andres Iniesta, Herrera is under no doubt that his compatriot remains on top.
"For me Iniesta is the only one. I like to play against him so I can tell my grandchildren about it.
"Arsenal have Coquelin, Ozil… Mesut isn’t so consistent, but he makes the difference when he’s on his day."