This study provides new evidence on changes in a range of online activities due to the Coronavirus disease (COVID-19) pandemic. Online activities replaced physical participation in activities and contributed to changes in urban mobility during the pandemic. Using data from a nationwide survey in Greece, the paper examines changes in the importance and the frequency of engaging in online activities before and during COVID-19. Findings show that both the importance and the frequency of engaging in telework, teleconferencing, online learning (e-learning), telehealth, and online shopping (e-shopping) significantly increased during COVID-19 compared to pre-COVID-19. Substantial increases in importance were reported for telework (31% increase), teleconferencing (34% increase), online learning (34% increase), and telehealth (21% increase). Those who, on a daily basis, teleworked, teleconferenced, and made video calls with family or friends quadrupled during COVID-19, while daily online learners increased seven-fold. Telehealth and online shopping also increased but more modestly. Urban mobility in the post-COVID-19 era is likely to depend on the degree of prevalence and acceptance of these remote online activities, together with a set of complex and interconnected factors related to urban form, the spatial planning and decision-making system, and social awareness about the future of cities.