Benefits related to health promotion by getting closer to forests have received increasing attention in modern stressful society; however, evidence-based research about how our brain activity changes when we stay in a forest environment is limited. Thus, the goal of this study was to evaluate the influence of viewing real forest landscapes on the activity in the prefrontal cortex area of young women’s brains. The experiment included 29 women (age: 21.0 ± 1.4 years) and was executed in five forest and five urban areas. The participants stayed in the forest and urban areas and viewed each view for 15 min. While viewing scenery, they had the oxyhemoglobin (oxy-Hb) concentrations in the left and right areas of their prefrontal cortexes measured continuously. Viewing real forest landscapes was associated with a significantly lower oxy-Hb concentration in the right area of the prefrontal cortex than when seeing urban areas. In conclusion, viewing real forest landscapes substantially diminished oxy-Hb concentrations in the right area of the prefrontal cortex, which is linked to physiological relaxation.