The paper focuses on the analysis of the dynamic response of the mechanical metamaterials manufactured using 3D printing technology. A modal analysis of a cantilever beam with a metamaterial segment was conducted to evaluate the influence of the segment geometry on the dynamic parameters of the structure, such as natural frequencies and mode shapes. A method allowing to include the effect of the actual stiffness of the beam support in the numerical model using elastic constraints was also proposed. The significant influence of the geometry of the metamaterial segment on the dynamic behaviour of the tested beam was proved. The research findings provided new insights that are significant for potential applications of metamaterials in civil engineering.