Is it code to have a concrete floor in a bedroom?
A concrete floor is not necessarily a sub-floor, it is may be considered a finished floor material. From Ground floor construction: "A ground-level floor can be an earthen floor made of soil, or be solid ground floors made of concrete slab.   Ground level slab floors are uncommon in northern latitudes where freezing provides significant structural problems, except in heated interior spaces such as basements or for outdoor unheated structures such as a gazebo or shed where unitary temperatures are not creating pockets of troublesome meltwaters. Ground-level slab floors are prepared for pouring by grading the site, which usually also involves removing topsoil and other organic materials well away from the slab site. Once the site has reached a suitable firm inorganic base material that is graded further so that it is flat and level, and then topped by spreading a layer-cake of force dispersing sand and gravel. Deeper channels may be dug, especially the slab ends and across the slab width at regular intervals in which a continuous run of rebar is bent and wired to sit at two heights within forming a sub-slab 'concrete girder'. Above the targeted bottom height (coplanar with the compacted sand and gravel topping) a separate grid of rebar or welded wire mesh is usually added to reinforce the concrete, and will be tied to the under slab 'girder' rebar at intervals. The under slab cast girders are used especially if it the slab be used structurally, i.e., to support part of the building."

From the Subfloor construction section: "Floors may be built on beams or joists or use structures like prefabricated hollow core slabs. The subfloor builds on those and attaches by various means particular to the support structure but the support and subfloor together always provides the strength of a floor one can sense underfoot. Nowadays, subfloors are generally made from at least two layers of moisture resistant ('AC' grade, one side finished and sanded flat) plywood or composite sheeting, jointly also termed Underlayments on floor joists of 2x8, 2x10, or 2x12's (dimensional lumber) spaced generally on 16-inch (40.6 cm) centers, in the United States and Canada."

Concrete slabs "may" be used as a sub-floor, but they also are of adequate quality to be considered a finished floor.

To really answer your specific question, you could check out the 1,244 page Ohio Building Code yourself.

I searched through it and see no specific provision saying that concrete is unsatisfactory as a finished floor... The only subfloor requirements I saw had to do with fire resistance, load bearing capabilities, and they all appeared to be related to wooden subfloors from my brief look over.