The increase in telecommuting during COVID-19 and advances in digital technology have necessitated the establishment of guidelines for maximizing productivity through indoor space design for telecommuters. Additionally, understanding the physiological response of individuals working in indoor spaces has attracted attention. This study applied mixed-reality environment to alter the design of the indoor space in real-time, while monitoring the task performance and representative psycho-physiological indicators (electroencephalogram and heart rate variability) of 30 individuals with telecommuting experience. To this end, four tasks, including spatial memory, attention, execution, and working memory, were conducted, and the psycho-physiological data from these tests were statistically analyzed. The results revealed that the design of the indoor space did not affect the spatial memory; however, the parasympathetic nerves were stimulated in visually non-preferred spaces, thus reducing mental stress and leading to high efficiency in short-term work. According to the Yerkes-Dodson law, the working memory of an individual is generally efficient and physically stable over time if they adjust to a preferred or decision-making space. Thus, the future design of telecommuting spaces must consider the type of work being done, and guidelines for spatial design should be developed by recognizing the psycho-physiological status of users, while increasing efficiency.