First let me establish that I personally hate the EPA. Their laws don't let me play with radioactive things in a home lab
Just as some amounts of sunlight is safe, some amounts of radon are. This is extremely small however, since radon is highly radioactive. Radiation causes mutation in genes, often leading to cancer. If there was a high concentration of radon, then you are extremely likely to develop cancer. If you really wanted to, you could set up a lab experiment and get the data for yourself. Avoid high concentrations of radon at all costs, unless you actually want to get cancer.