As of August 2011, Mel Gibson has been arrested once, for DUI (Driving Under the Influence) and for making antisemitic remarks to the cop who arrested him. This happened in Malibu on 28th July 2006. At the court hearing, Gibson pleaded no contest and was handed three years probation, restrictions were imposed on his driving license for 3 months and he had to pay a fine of $1300. He was also directed to attend a program for First Attenders as well as self-help meetings. More information can be found here: http://www.ask.com/wiki/Mel_Gibson#Alcohol_abuse_and_legal_issues
Surprisingly, there is only 1 publicly recognized arrest for Mel Gibson. That was on July 28, 2006 for a DUI. He has come close to being arrested on numerous occasions. His controversial life can be read about in his biography at http://www.ask.com/wiki/Mel_Gibson.
Mel Colm-Cille Gerard Gibson has had a run in with the law at least five times and been arrested at least two times. Although his arrests get a lot of press, many Hollywood bad boys have been arrested dozens of times.