The SFO and City of London Police arrested three men aged 33, 41 and 47 after searching a house in Surrey and two in Essex.
The three were taken to a London police station to be interviewed "in connection with the investigation into the manipulation of Libor".
The SFO's investigation into Libor rigging was sparked by the £290m fine levied on Barclays in June, which led to the departures of the bank's chairman Marcus Agius, chief executive Bob Diamond and newly prompted chief operating officer Jerry del Missier.
The SFO did not name the men or say where they were employed.
The director of the SFO, David Green, has told MPs that he knows the agency will be largely judged on the success of the Libor investigation and had deployed 40 staff on the cases which involve more than one firm.
The SFO announced a formal investigation into the complex rate-rigging affair on 6 July but by the end of that month had already concluded that it had the powers to conduct a criminal investigation.
While the Financial Services Authority and regulators in the US have fined Barclays, individuals involved had not been formally named or reprimanded by the FSA. Barclays head of investment banking Rich Ricci told the banking standards committee that it had "terminated the employment of five people and that 13 staff had been disciplined in total.
Baclays is so far the only bank to have been penalised by the regulators although speculation is rife that other banks will face penalties before the end of the year. The FSA said that eight financial firms in total, and not just banks, were the subject of investigations by the City regulator.
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