- guardian.co.uk, Thursday 23 April 2009 16.33 BST
Johnson said the majority of police had done a "fantastic" job in difficult circumstances during the protests, which brought the City to a standstill earlier this month.
The Metropolitan police has faced heavy criticism since the Guardian obtained footage of Ian Tomlinson hitting the ground after being pushed by a police officer.
Moments later, Tomlinson, a 47-year-old newspaper seller who had not been involved in the protests, collapsed and died.
A second post mortem found he had not died of a heart attack – the conclusion of the first examination – but from internal bleeding.
In an interview with Jon Gaunt on SunTalk radio, Johnson said: "I worry that there are large sections of the media that are currently engaged in a very unbalanced orgy of cop bashing.
"I think it is wrong, it is wildly overdone ... everybody understands that there are serious questions to answer about what happened to some of the protesters at the G20, and particularly Ian Tomlinson, and thoughts are with his family, but you have to get it into proportion."
At the time of the interview, Johnson was preparing to travel to a private meeting with the Metropolitan police authority to discuss the force's handling of the protests.
The Territorial Support Group, the Met's specialist unit responsible for crowd control, is at the centre of the controversy.
The Independent Police Complaints Commission is currently investigating the unit over the death of Tomlinson and an alleged assault on a woman in the crowd.
Johnson's criticisms were prompted by Gaunt, who said a friend of his was a serving armed response officer in the Met and had told him morale in the force was at an all-time low.
"Everyone in London feels sympathy for Ian Tomlinson's family. But the fact is the huge majority of police do a fantastic job," Johnson said.
"They were faced with very difficult circumstances when they were asked to police the G20 summit and overwhelmingly it was an extremely good job that they did.
"I think the police deserve a fantastic amount of credit they are not getting at the moment."
Johnson also said he supported Sir Paul Stephenson's decision to discipline any officer who refused to display their number.