Radon is a radioactive gas found naturally throughout the country that's created by the decay of uranium found in rocks and soil.
It is invisible, odorless and tasteless, but easily detected by professionals or with do-it-yourself kits, Health Canada said in a release.
The caution was issued as winter approaches and homes are closed up and have less ventilation.
The agency said research earlier this year showed radon exposure was responsible for 16 percent of all lung cancer deaths in the country, second only to smoking.
Various studies done across the country in the past few years showed an average of 5 percent of Canadian homes have more than the acceptable level of 200 becquerels per cubic meter, the agency said.
While homeowners can conduct their own tests, professional help is required in venting and preventing the recurrence of radon build-up, the report said.