In recent years, working styles have become more diverse, and places and hours of work have been changing rapidly. Determination of worker mental states and productivity using conventional, questionnaire-based surveys is difficult. We continuously measured biometric data using a wristband device. The study objectives were as follows: devising a method for estimating worker mental states using biometric data; understanding the relationship between worker mental states and workplace productivity; and evaluating the effects of workplace behavior and communication on mental states during office work. In this study, biometric data were measured using wristband devices; questionnaires on workplace productivity, behavior, space, and communication were administered to workers in an office where activity-based work was introduced. Based on the heart rate and low frequency/high frequency (LF/HF) ratio (an index of autonomic nervous system activity), we estimated the mental states of office workers in the four quarters: stressed/excited, concentrated, relaxed, and aroused states. Correlation with workplace productivity was confirmed in the concentrated state. The study confirmed that workplace productivity of office workers varied with behavior type, workspace, and communication. In the future, this method is expected to enable the objective evaluation of various spaces.