Fidelity said Monday that its customers remained calm during the market plunge and many took the opportunity to buy.

The company's website appeared not to have issues, in contrast to reported outages at T. Rowe Price and robo-advising firms Wealthfront and Betterment.

"From a retail perspective, definitely more buyers than sellers today," Keith Bernhardt, vice president of retirement and college products at Fidelity, said in a phone interview with CNBC. "We're not really seeing panic."

The company did not have exact data to share as of Monday evening, but said anecdotally that levels were similar to Friday, which saw 52 percent more buys than sells.

The fell 4.1 percent Monday in its worst day in more than six years, following a 2.1 percent drop Friday. The Dow Jones industrial average briefly tumbled more than 1,500 points Monday into correction territory, or 10 percent from a recent high, but closed 1,175 points lower after falling nearly 666 points Friday.

There was no specific driver behind Monday's market plunge, which followed stocks' worst week in two years as traders worried about rising interest rates.

Fidelity has 26 million individual customers and $6.2 trillion in total customer assets as of June 30, according to the company's website.

"People are recognizing that the market has had a tremendous upwsing," Bernhardt said, noting that a market correction has been due for a while.

"I can't say anything's changed based on a day or two," he said. "People are paying attention, calling in, trying to get some guidance."