Radon levels rise and fall inside a house, so it is quite difficult to gauge how serious the issue is on your own. Use local service for the test. After radon been tested by professionals and found. There are plenty of options available to reduce its level or cut the source.
A single dehumidifier won't help much with radon.
If a house has serious Rd issues, a radon mitigation system has to be installed, which is costly or an alternative solution - like a radon mitigation fan, if your Rd level is slightly higher than the norm and fan was recommended by the technician.