Background: From March to May 2020, lockdown measures were adopted in Italy to contain the epidemic of the novel Coronavirus. People were forced to restrict their movement and social contacts, therefore having a higher risk of inactivity. This study, carried out among Italian undergraduates, explored their sedentary and physical activities (PA) during the lockdown with respect to their previous habits. Methods: An electronic questionnaire was administered once to students attending three Italian universities after the end of lockdown. Results: A total of 1430 students (mean age 22.9 +/- 3.5 years, 65.5% females) completed the questionnaire. All the sedentary behaviors increased significantly, and all the physical activities decreased significantly during the lockdown. Time spent using electronic devices showed the highest increase (+52.4 min/day), and walking the greatest decrease (-365.5 min/week). Being younger than 22 years old, female, and previously active, attending the universities of Naples and Rome and having at least one graduate parent were associated with the achievement of recommended levels of PA even during the lockdown. Conclusions: This study highlights the reduction of PA among Italian undergraduates in the course of home-confinement due to the CoViD-19 pandemic. The practice of adequate PA during the lockdown was mainly associated with the previous adoption of an active lifestyle. Promoting active lifestyles during the non-pandemic period may have had positive effects also in case of lockdown.