Ferguson was charged with improper conduct, relating to his pre-match media comments made about Webb ahead of Manchester United's key Premier League encounter with Chelsea on May 8.
Ferguson is not believed to have offered a significant response to the charge.
And on Monday he has learned he will face no punishment, beyond a gentle reminder not to do it again.
"A Regulatory Commission has today warned Sir Alex Ferguson as to his future conduct," said an FA statement.
"Ferguson was charged with improper conduct, relating to his pre-match media comments made about match official Howard Webb on May 6, 2011.
"The chairman of the commission made the following statement following the hearing: 'This rule was brought in at the start of the 2009/10 season and this was reiterated formally to all Clubs again on 21 October 2010.
'This is a clear breach of the rule and it is the first time such a matter has been placed in front of a Commission."