We theoretically demonstrate electrically controlled light focusing using a tunable metasurface employing thin film lithium niobate (TFLN). The designed metasurface features a high-quality factor guided-mode resonance with an electrically controllable resonant wavelength, resulting in a high extinction ratio of transmittance at the operational wavelength by changing the applied voltage. A reconfigurable one-dimensional Fresnel zone plate with a focusing efficiency of around 15% has been realized through spatial modulation of transmitted light intensity, whose focal position can be electrically tunable in both longitudinal and lateral directions. Our approach reveals the great potential of metasurfaces using TFLN for electrically controlled light focusing.