Background The outbreak of the COVID‐19 pandemic has negatively affected the lives of many people. In particular, restrictions of physical activity (PA) due to pandemic‐related lockdown have impacted their psychological status. The aim of this work was to investigate the relationship between PA habits, before the pandemic and during the lockdown, and responses to stress due to home isolation during the lockdown, in older people. Methods To this aim, an online survey addressed to people aged 65 years and over was conducted during the first pandemic wave in Italy (Study 1). To explore the effect of PA restrictions on responses to stress over time, the survey was replicated during the second wave (Study 2). A group of 72 and 43 participants, from 65 to 88 years, completed the two studies, respectively. The survey required the completion of the International Physical Activity Questionnaire, and of two questionnaires on stress response, namely, the Impact of Event Scale‐Revised and the Perceived Stress Scale. The correlation between the questionnaires' scores was examined. Results Study 1 demonstrated that higher levels of PA during the lockdown, related to working and walking activities, were associated with fewer stress‐related symptoms and lower stress perception. In parallel, greater reduction of PA, during lockdown compared to the pre‐pandemic period, was associated with more stress‐related symptoms. People who spent more time at rest (sitting) before and during the pandemic lockdown were those who showed higher psychological impact. Study 2 confirmed the benefits of maintaining working activities during lockdown, but also showed that during the second pandemic wave people were more resilient to PA restrictions and home isolation, even if conducting a sedentary lifestyle. Conclusions Maintaining good levels of PA during lockdown was a protective factor against developing stress‐related symptoms in older people. On the other hand, more resilient response to stress emerged in this population during the second wave.