Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 19 (COVID-19), has resulted in dramatic changes in human lifestyles and the geographic distribution of populations. However, despite the unequal impact of COVID-19 across urban spaces, research on the association between socioeconomic disparities in the usage of various types of urban amenities during the pandemic is limited. Thus, this study utilized mobile phone data and land use/land cover (LULC) data to investigate COVID-19-induced changes in the hot spots of the daytime and nighttime populations of two districts in Seoul, South Korea: Gangnam (a high-income community) and Gangbuk (a low-income community). First, the differences between Gangnam and Gangbuk in the LULC and mobile phone data, before and during the pandemic, were statistically analyzed by age. Second, the areas with significantly increased mobile phone-based populations during COVID-19 were identified using a hot spot analysis method and Welch’s t-test. This study identified that there were significant disparities in the use of green spaces during the pandemic, with a higher percentage of the mobile phone-based population in Gangnam than Gangbuk. Youths and adults in Gangnam were more likely to visit schools and enjoy physical activities in forests and open spaces during the pandemic, whereas there was no such increase in Gangbuk. The findings contribute to the understanding of the impact of COVID-19 on human behaviors and socioeconomic disparities in the quality of urban life.