Legally, yes, on a home you own or lease: Ohio's licensing law exempts owners working on their own building. Anyone you pay must hold an ODH mitigation contractor license. The hard parts are diagnostics, sealing, fan placement, and the discharge rules.
More detail
The owner exemption sits in ORC 3723.02 and covers testing and mitigating your own property. It does not make a homemade system match the Ohio Radon Mitigation Standards, which a buyer's inspector may hold it against later. Those standards keep the fan in an attic, a garage not under living space, or outside, never in a basement; put the discharge above the highest eave and at least 10 feet from nearby windows, doors, and a neighbor's openings; require a fan whose maker lists radon use; and call for a backdraft check wherever natural-draft gas appliances share the basement. If you go it alone, get a proper post-mitigation test and keep notes and photos, because the next owner will ask. Most people who price the parts, the roof work, and the diagnostics decide an installed system is the better trade.