The magnetic properties of host-guest systems composed of a nanoporous network of curved sp 2-nanocarbon sheets are investigated by using zeolite-templated carbon (ZTC) as a host material with focus on the effects of aging after synthesis, the presence of the template, and guest adsorption. There are two kinds of localized magnetic moments originating from a radical state at a curved part and an edge state at an edge part of the individual nanocarbon sheet. The ZTC sample just after synthesis shows an antiferromagnetic transition at 13 K, which disappears through aging process under ambient gas species such as oxygen. On the other hand, the template removing process during synthesis by using non-oxidizing reagent does not influence the magnetism of ZTC. The results of bromine adsorption reveal that a curved part responsible for the radical state in ZTC is destroyed through chemical reactions with the electron-accepting species. Potassium adsorbed into the nanopores in ZTC, forms magnetic clusters which undergo a ferromagnetic transition at 24 K. The ZTC spins well decoupled with the potassium spins act as a probe in observing the magnetic behavior of the guest potassium.