The move comes as the price of bitcoin soars with some experts predicting the cryptoasset bubble will soon burst.
The price of one bitcoin, for example, has topped £25,000 in recent days.
The FCA says it is aware of some firms offering investments in cryptoassets, or lending products or investments linked to cryptoassets, that promise high returns.
Since yesterday (10 January), all UK cryptoasset firms must be registered with the FCA under regulations to tackle money laundering. Operating without a registration is a criminal offence.
The watchdog has warned consumers that investing in cryptoassets, or investments and lending linked to them, generally involves taking “very high risks” with their money.
It warns that if consumers invest in these types of product, they should be prepared to lose all their money.
It says investors must treat crypto-asset linked investments as “high-risk, speculative investments” and make sure they know what they are investing in.
Cryptoasset-related investments are unlikely to be covered by the Financial Ombudsman Service (FOS) or the Financial Services Compensation Scheme (FSCS) if something goes wrong.
The FCA issued a guide to cryptoassets in PS19/22: Guidance on Cryptoassets.
The regulator says consumers should be particularly wary if they’re contacted out of the blue and pressured to invest quickly or promised returns that sound too good to be true.