At a Phoenix news conference, the right-wing senator claimed illegal immigrants light fires in the wilderness for warmth, to send signals and to distract border agents, CNN said.
"There is substantial evidence that some of these fires have been caused by people who have crossed our border illegally," McCain said. "The answer to that part of the problem is to get a secure border."
However, he offered no evidence to substantiate his claim.
Civil rights advocate Randy Parraz told CNN such unfounded allegations were "careless and reckless" and said McCain was trying to make rightist political headway with the wildfire crisis.
"It's easier to fan the flames of intolerance, especially in Arizona," Parraz said.
High heat, low humidity and steady winds have helped dozens of fires in Arizona consume more than 700,000 acres of land in the past three weeks.