There has been a "spectacular" increase in retail investor activity, thanks in part to cryptocurrencies and marijuana-related securities, TD Ameritrade CEO Tim Hockey told CNBC on Tuesday.

Helping fuel that growth is millennials. New accounts from clients ages 35 and younger jumped 72 percent in the fourth quarter compared with a year earlier.

"Right now there is frenetic activity from a retail trade point of view," Hockey said in an interview with "Closing Bell."

So far this month, TD Ameritrade is doing about 975,000 trades a day.

After the bell Monday, the e-trader reported fourth-quarter earnings and revenue that beat analyst expectations. Its daily average trades were 726,000 in the fourth quarter, up 49 percent from a year earlier.

The cryptocurrency and marijuana sectors made up about 7 percent or 8 percent of those trades, Hockey said. A year prior, they made up about 2 percent, he said.

The peak came in December.

"We all saw it, right? We went to holiday parties. Everybody was asking about your opinion around cryptocurrencies, blockchain," he said.

TD Ameritrade recently announced it was extending trading hours on its platform to 24 hours, five days a week for several popular exchange-traded funds. Hockey said the move makes sense because market-moving events happen overnight.

— Reuters contributed to this report.