Howard Marks believes top investors can still thrive even as trading machines become more active in the financial markets.

"Computers can do an unmatched job dealing with the things that can be counted: things that are quantitative and objective. But many other things — qualitative, subjective things — count for a great deal, and I doubt computers can do what the best investors do," Marks said Monday in a note to clients entitled "Investing Without People."

Marks, whose firm, Oaktree Capital, had $121 billion of assets under management as of March, said computers can't do things such as meet and assess management teams, listen to venture capital presentations and look at buildings for real estate investments.

"The greatest investors aren't necessarily better than others at arithmetic, accounting or finance; their main advantage is that they see merit in qualitative attributes and/or in the long run that average investors miss," he said. "And if computers miss them too, I doubt the best few percent of investors will be retired anytime soon."

Marks is known for his prescient investment memos, which warned about the financial crisis and the dot-com bubble implosion.

The Oaktree co-chairman noted computers can help investors make more informed decisions, but they won't replace human insight.

"Computers, artificial intelligence and big data will help investors know more and make better quantitative decisions. But until computers have creativity, taste, discernment and judgment, I think there'll be a role for investors with alpha," he said.

Marks has a net worth of $1.9 billion, according to Forbes.