Uber's $40 billion valuation seems high, but the pre-IPO investment market has changed considerably from 2000, just before the tech bubble's burst, Carlyle Group co-founder and co-CEO David Rubenstein told CNBC on Tuesday.
"It does seem high, but remember, a lot of people thought Facebook's valuation before it went public was high, and it was much higher than that, actually," he said in a "Squawk Box" interview. "A lot of people have made money on companies like Facebook before they went public, and now people feel that investing in these companies before they go public is probably a pretty good bet."
Rubenstein noted there are roughly 75 companies with billion-dollar valuations today.
Sentiment will surely change after the first of these companies experience a dotcom bubble-style failure, he said. For the time being, investors feel that companies with international brand recognition such as Uber are not going to go away overnight, he added.
Most of the billion-dollar companies getting ready to go public today are more financially sound and actually have much lower valuations than some of the tech start-ups in the late '90s, Rubenstein said.
"They have revenues, they have earnings. That was not the case in 2000," he said.
On Monday, the Nasdaq closed above 5,000 for the first time since the tech bubble popped. Rubenstein said the milestone is actually not a big deal because the Nasdaq would have to reach about 7,000 in order to hit its peak in inflation-adjusted terms.