The left-wing activist argued the way the Mayor of London acted turned people into jihadists.
Jihadi John – born Mohammed Emwazi – was the Kuwait-born, London-raised ISIS executioner killed by an American drone strike last year.
On a video he uploaded to his Facebook page, Brand said: “”The mentality of Boris Johnson creates more problems, the allegiances of Boris Johnson create more problems.
“The activities of organisations that he belongs to, that he supports, create these problems.
“Boris Johnson grows Jihadi Johns – he is a Jihadi John machine.
“Jihadi John is just one.
“Once Jihadi John is dead that”s the end of Jihadi John but Boris Johnson can create thousands of others.”
However, fans of the comedian were quick to tell him just what they thought of his bizarre rant.
Richard Finlay wrote: “Would love Russell to explain how Boris Johnson grows Jihadi Johns. Is he under the impression Boris devised the Quran and the Hadiths and jihadist ideology?”
Tommy Exoque Stevenson took it a step further, claiming Brand was “a f****** idiot”.
He said: “Only politics he knows about is bankers’ bonuses, hence why even the crowd on [BBC show] Question Time silences his idiotic views.
“Stick to shouting on the street, you have no idea what you’re talking about in your liberal rich ivory tower.”
Carlos Heath Russell wrote on his Facebook page: “I respect your Green attitude but if you think for one second that a Jihadi Jon (sic) wouldn”t think twice about cutting your head off with a knife because it would get media attention then think again.
“The difference between Mr Johnson and Jihadi Jon is that Boris wouldn”t even contemplate such inhumane acts.”
The 40-year-old, who was once married to pop star Katy Perry and called for political revolution before the last election, last month moved to a £3million home in well-heeled Henley-on-Thames, Oxfordshire – Mr Johnson’s former constituency.