This study evaluated the Indoor Environmental Quality (IEQ) performance of a net-zero energy office building in a mixed-humid climate during its first year of operation. The IEQ assessments included an occupant IEQ satisfaction survey and continuous measurements of selected IEQ variables with occupancy using a detailed IEQ monitoring cart. As a result, this study found many compelling evidences that low energy buildings can deliver high standards of comfort to their occupants. The surveyed occupant satisfaction with thermal comfort, air quality, and lighting were higher than comparable benchmark values, which is a notable achievement when considering the fact that the building used natural ventilation and daylight systems. The study also found that the case-study building's natural ventilation system provided thermal conditions comparable with air-conditioned modes, while providing between 70% and 90% savings of the total conditioning energy.