Indoor air quality has a crucial influence on the well-being of people present in a given room. It is mostly determined by temperature and humidity, which determine the thermal comfort and microclimate of the room, as well as the feeling of people in the room. Another important parameter of indoor air quality is the concentration of carbon dioxide. High carbon dioxide concentration is common in teaching rooms and can lead to decreased cognitive performance especially reasoning, short-term memory, concentration and verbal ability of a person present in such room. The aim of this research is to analyze the concentration of carbon dioxide in a teaching room with the same physical activity of people in it, depending on temperature and relative humidity of the indoor air. For the analysis was selected a teaching room in a higher education istitution located in central Poland, in a temperate climate. The concentration of carbon dioxide, relative humidity and temperature were measured in the room. The assessed indoor air quality parameters, i.e. temperature and humidity, varied depending on date and duration of the measurements, while still meeting the standards for teaching rooms. The greatest changes were observed in the values of carbon dioxide concentration - it exceeded the values recommended in the standards increasing during the measurements and undoubtedly affecting the ability to conduct classes. Furthermore, a high positive correlation was found between carbon dioxide concentration and temperature in the analyzed teaching room.