The Cook County judge on trial this week for fraud may have made mistakes, her attorney said Tuesday.

But so did the government when it indicted her, he added.

“Mistakes are not fraud,” he said.

Ricardo Meza made his comments as the trial of Judge Jessica Arong O’Brien kicked off in earnest Tuesday morning with opening statements at the Dirksen Federal Courthouse. The feds said O’Brien pocketed $325,000 as she lied to lenders amid a $1.4 million scheme involving two South Side properties between 2004 and 2007.

“Ultimately, that is what this case is about,” Assistant U.S. Attorney Matthew Madden said. “The defendant’s lies.”

O’Brien would likely lose her seat on the bench — not to mention face serious prison time — if convicted at the end of what is expected to be a two-week trial. Neither attorney mentioned O’Brien’s job during opening statements, and none of the allegations relates to her office.

The feds have said they don’t plan to mention it, unless she testifies.

Still, jurors found U.S. District Judge Thomas Durkin’s courtroom suddenly packed with onlookers for what is expected to be a dry trial revolving around mundane paperwork produced by transactions that happened more than a decade ago.

Jurors got a glimpse of that paperwork during Madden’s opening statement. The prosecutor accused O’Brien of repeatedly lying as she bought, refinanced and sold properties in the 600 block of West 46th and 800 block of West 54th.

Madden said O’Brien overstated her income as she applied for loans and at one point failed to mention a $260,000 mortgage on her primary residence. Then, after selling the properties to a co-worker named Maria Bartko through a straw buyer, Madden said O’Brien made two undisclosed payments to Bartko totaling $73,000.

Bartko, who was a licensed loan originator, pleaded guilty to her role in the alleged scheme last month.

Meza said O’Brien is not guilty, and he wound up mocking the feds’ allegations. At one point, he waved copies of the detailed checks his client wrote to Bartko in the air, telling jurors that, “the only thing she left off there is ‘kickback check.’”

The defense attorney noted that simple credit reports would have caught many of the lies prosecutors accused O’Brien of telling. And even though Madden said O’Brien once claimed an $81,000 annual income in a year she wound up making $11,500, Meza said that was because she took unpaid maternity leave.

Finally, Meza insisted that even though the feds characterize O’Brien’s alleged crime as a $1.4 million scheme, he said that number comes from totaling up loans that O’Brien paid back.

“Whatever Jessica did, it was always done in good faith,” Meza said. “If she made a mistake, she’s no different than anyone else.”