ABSTRACT This study investigated the initial three-month impact of the COVID-19 pandemic on the explicit processes towards physical activity (PA). In addition, we explored whether potential changes in explicit processes are associated with changes in PA and sedentary behavior (SB). Seventeen older adults (aged 65.7 ± 3.8 years; 76.5% women) with hypertension were included in this longitudinal study performed in Natal, Brazil. Explicit processes (explicit attitude [perceived benefits and cons perceived], social norms, social modeling, self-efficacy, intention and motivation) were evaluated through self-reported questionnaire before (January to March 2020) and during (June 2020) the COVID-19 pandemic. In addition, PA and SB were measured by accelerometry during seven days. Generalized linear and mixed models were used for data analysis. There was a decrease in the explicit attitudes (β = – 4.8, p = 0.001) and moderate-vigorous PA (β = – 4.8, p = 0.035) during the COVID-19. Changes in the explicit attitudes were associated with the changes in the moderate-vigorous PA (β = – 1.6, 95% CI – 2.9, – 0.3, p = 0.034). No significant changes were found in the additional explicit process measures, time spent doing light PA and SB, and step count. Our findings may suggest that the COVID-19 pandemic has negatively impacted the explicit attitudes related to PA and contributed to decrease the time spent in the moderate-vigorous PA in older adults with hypertension.