The FCA did not name those who received the notices warning them of its intention to take action against them, nor did it name their institutions.
It said that in November it gave a warning notice to a submitter of interest rates for failings over two years, and another warning to a manager at a bank for issues over more than three years.
Previously regulators have focused on companies with several banks, including Royal Bank of Scotland, hit with fines over manipulation over benchmarks such as the London Interbank Offered Rate (Libor), while other cases remain outstanding.
From yesterday, Libor was set by New York Stock Exchange owner ICE which took over from the British Bankers' Association.
The submitter, the FCA said, made submissions that took into account requests from traders at his own and other banks and from an interdealer broker.
The submitter also approached other banks on behalf of traders.
In the case of the manager at a bank, he was aware of, and condoned, traders making requests to submitters to manipulate interest rate benchmark submissions.
He was also aware of submitters, who reported to him, making submissions that took those requests into account.
The FCA was given the power to issue warnings in October.