Mr McAfee made the offer to the FBI in an article published by Business Insider.
Apple has refused to comply with a court order asking it to unlock the device, dividing opinion over whether the firm should be compelled to do so.
Mr McAfee said he and his team would take on the task “free of charge”.
The offer came as Mr McAfee continues his campaign as a US presidential candidate for the Libertarian Party.
“It will take us three weeks,” he claimed in his article.
Security expert Graham Cluley told the BBC he was sceptical of Mr McAfee’s claims.
“The iPhone is notoriously difficult to hack compared to other devices,” he said.
‘Dead men’s tales’
For instance, Mr Cluley cast doubts on Mr McAfee’s idea that he could use “social engineering” to work out the pass-code of Farook’s locked iPhone.
This is a process by which hackers try to find out login credentials by tricking people into giving them away.
“In a nutshell, dead men tell no tales,” said Mr Cluley. “Good luck to Mr McAfee trying to socially engineer a corpse into revealing its pass-code.”
“The FBI isn’t interested anyway, they want to set a precedent that there shouldn’t be locks they can’t break,” he added.
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