"They made one mistake," the billionaire investor says.
"They made one mistake," Buffett said in a " Squawk Box " interview. "Incentives work. And they came up with improper incentives and they worked. And, so, they [incentivized] bad behavior instead of [incentivizing] good behavior. And that happens from time to time."
Wells Fargo's stock was up 1 percent in premarket trading.
Wells admitted that as many as 3.5 million accounts were created for customers without their permission. That's nearly 70 percent more than originally thought. The scandal led to the departure of multiple executives, including former CEO John Stumpf.
The bank said Friday that it settled a class action securities fraud lawsuit for $480 million. Wells denied claims in the suit and that it settled to avoid further cost and disruption.
Buffett, who is an investor in Wells Fargo, has previously said the bank's woes aren't likely to influence his investment long term. "It's a terrific bank," he said in August. "There were some things that were done very wrong there but they are being corrected."
On Monday, Buffett said that he doesn't know the details about why the bank's practices weren't stopped sooner but said other companies have had similar troubles.
The Oracle of Omaha noted that if an investor looked at the record of Wells Fargo 10 years from now, they're likely to see it perform better than it's peers.
"Going forward, you can stop bad practices. They should be stopped earlier," Buffett said from Omaha, where Berkshire Hathaway held a weekend of events around Saturday's annual meeting.
Buffett and his longtime investing partner and vice chairman, Charlie Munger , spoke to the tens of thousands attendees on a wide range of topics from their massive stake in Apple to missing out on Google and Amazon to bashing bitcoin as "rat poison."
— Buffett joins "Squawk Box" for three hours, 6 a.m. ET to 9 a.m. ET, with special guests Munger and Microsoft co-founder and philanthropist Bill Gates .
With Berkshire's 2018 annual meeting in the books, users can revisit the highlights in CNBC's Warren Buffett Archive, which houses searchable video from 25 full annual meetings, going back to 1994, synchronized to 2600 pages of transcripts. The Warren Buffett Archive also includes 500 shorter-form videos arranged by topic, CNBC interviews, a Buffett Timeline, and a Berkshire Portfolio Tracker.