Campaigners say the messages will provide a "reassuring" antidote to religious ads that "threaten eternal damnation".
Professor Dawkins, the author of The God Delusion, said: "Religion is accustomed to getting a free ride - automatic tax breaks, unearned 'respect' and the right not to be 'offended', the right to brainwash children.
"Even on the buses, nobody thinks twice when they see a religious slogan plastered across the side. This campaign to put alternative slogans on London buses will make people think - and thinking is anathema to religion."
The advertising campaign, which could be plastered across as many as 60 buses for a month if just £11,000 ($27,000) is raised, was triggered by a blog posting. Those behind the project are confident they will raise enough money to pay for two sets of 30 bendy buses to travel through the capital in January bearing the atheist slogan: "There's probably no God. Now stop worrying and enjoy your life."