Many studies have been performed to accelerate osteoinduction and osteoconduction into porous ceramic scaffolds by seeding them with cells. In this study, we compared available cell-seeding methods on a porous ${eta}$-tricalcium phosphate (${eta}$-TCP) scaffold and evaluated the effects of cell-seeding on the mechanical properties of the porous ${eta}$-TCP scaffold. Three types of porous bioceramic scaffolds were used: dry scaffold, scaffold wetted with media, and scaffold cultivated with normal human osteoblasts (NHOs). Cell-seeding into the porous ${eta}$-TCP scaffolds was performed by conventional, centrifuge, high-density, and vacuum methods. After confirming cell proliferation with MTT assay and cell staining, a compressive test was performed after 2 and 4 weeks of cell culture. The vacuum method based on the high-density cell culture inserted effectively NHOs into the ${eta}$-TCP scaffolds. The compressive elastic modulus of wetted ${eta}$-TCP scaffolds decreased significantly ( p < 0.05) about 20~30% after 2 and 4 weeks of incubation in comparison with that of the dry scaffold. However, the compressive strength of the scaffolds cultivated with NHOs for 3 weeks was significantly (p < 0.05) higher than that of scaffolds without NHOs. The vacuum with the high-density of cell-seeding seems to be a suitable method for seeding cells into complex porous ceramic scaffolds. Cell proliferation and uniform distribution in the scaffolds can change the initial mechanical properties of porous ceramic scaffolds.