"It's important to make sure that it is not used as a vehicle for illicit transactions and that there is investor protection," Yellen added.
When asked about the Gamestop frenzy, Yellen replied that at the moment it is hard to tell whether stimulus checks spurred the investments or not, but the broad conclusion was that markets held up reasonably well and the core infrastructure was resilient, despite high volatility.
A Reddit-fueled day-trading craze last month pushed shares of GameStop Corp., the videogame retailer, as high as 483 dollars, but the hype has fizzed. Shares traded Thursday around 50 dollars, off almost 90 percent over the past two weeks.
Interest has diminished on WallStreetBets, the forum that sparked the frenzy, and trading volume and short interest have tumbled as well.