If their value fell sharply, it could have a knock-on effect, he said.
The Bank needed to be ready to contain those risks, he added.
Speaking to the BBC’s Today programme, Sir Jon said that at present, about 0.1% of UK households’ wealth was in crypto-currencies.
About 2.3 million people were estimated to hold them, with an average amount per person of about £300.
However, he stressed that crypto-currencies had been “growing very fast”, with people such as fund managers wanting to know whether they should hold part of their portfolios in crypto-currencies.
“Their price can vary quite considerably and they could theoretically or practically drop to zero,” he said.
“The point, I think, at which one worries is when it becomes integrated into the financial system, when a big price correction could really affect other markets and affect established financial market players.
“It’s not there yet, but it takes time to design standards and regulations.”
He added: “We really need to roll our sleeves up and get on with it, so that by the time this becomes a much bigger issue, we’ve actually got the regulatory framework to contain the risks.”
Read More: Here