Abstract Background The Square Stepping Exercise (SSE) is an exercise training program incorporating cognitive and physical exercise components, which was originally developed for older adults to reduce falling risks. SSE’s potential in delaying cognitive decline in older adults seems to be promising. However, there is scarce research on the SSE program with young adults. Furthermore, the outbreak of coronavirus disease has imposed people to change their lifestyle and behaviors, including exercise behaviors. Hence, the purpose of this study was to examine the acute effects of a home-based online SSE trial on cognitive and social functions in sedentary young adults. Methods A total of 18 young adults (6 males, 12 females) participated in the present study. They completed two exercise conditions (SSE and active control exercise), consisting of 3 sessions per week, over 2 weeks. A 2 times (pre vs. post) × 2 conditions (SSE vs. active control) repeated-measures ANCOVA was conducted on the score of the Modified Card Sorting Task with age and education year as covariates. A one-way repeated-measures MANOVA was performed on the subscale scores of the Physical Activity Group Environment Questionnaire to examine the effects of the exercise conditions (SSE vs. active control) on group cohesion. Results SSE was found effective to improve executive function such as abstract reasoning, mental flexibility, and problem-solving skills. Furthermore, participants’ perceptions of social interaction with their group, and closeness and bonding existing in their group were significantly higher in the SSE condition than the active control condition. Conclusions In the present study, SSE was conducted online and found to be effective to enhance executive function and group cohesion in sedentary young adults. These novel approach and findings are the strengths of the present study. People aged 60 years and over are more vulnerable to the coronavirus and at higher risk of developing serious illness. Given the coronavirus pandemic circumstances, it is worthwhile to explore the possibility of the online SSE approach to older adults in future research.