The chief executive of Tesla Inc, whose recent tweets have fueled the digital-currency rally, made the remark on Twitter while replying to a user who said that gold was better than both bitcoin and conventional cash.
Musk, who earlier in the week remarked that he found the prospect of holding bitcoin adventurous for an S&P 500 company, said in a tweet: "Money is just data that allows us to avoid the inconvenience of barter ..."
"That said, BTC & ETH do seem high lol," he added.
Bitcoin, the world's most popular cryptocurrency, hit a fresh high in Asian trading on Saturday, extending a two-month rally a day after the digital currency's market capitalisation exceeded $1 trillion.
Ethereum or ether is the second-largest cryptocurrency by market capitalisation and daily volume.
Musk, an ardent proponent of digital currencies, has defended Tesla's recent purchase of $1.5 billion of bitcoin, which has ignited mainstream interest in the digital currency.