Bitcoin is a fad, just like bimetallism before it, according to one Nobel Prize-winning economist.

The observation came from American economist Robert Shiller, who compared the cryptocurrency to the bimetallism fad of the late 19th century when both gold and silver were accepted as legal tender.

"I'll take bitcoin, too, because I know I can sell it and get out of it. There seems to be some strange enthusiasm for it," Shiller said on CNBC's "Closing Bell." "People get excited about things like new monetary standards. Remember bimetallism? It went into a fad, everyone was talking about it for a while. And then it faded."

Bitcoin hit a record high of $5,856.10 on Friday, according to data from industry website CoinDesk. Its market capitalization, which is the total value of all the bitcoin in circulation, reached $96.7 billion, according to Coinmarketcap.com.

"I think gold is a bubble, but it's always been a bubble," hedged Shiller. "It has some industrial uses, but it basically it's like a fad that's lasted thousands of years."

On the markets front, the economist noted that he's seeing some worrying signs in his data around the anniversary of the fateful 1987 stock crash.

"Confidence in the valuation of the market is indeed the lowest it's been since 2000," warned the economist. "And when it got low in 2000, the market fell about 40 percent. So it was bad."

"I think there's a danger, but I'm not saying to sell everything. I'm still in the market myself."