The management of chronic diseases (CD) includes physical activity (PA). It is necessary to determine the effects of COVID-19 restrictions in CD. The aim was to review the research related to PA levels before and during the COVID-19 pandemic in people with CD. This review was designed according to PRISMA guidelines and registered in PROSPERO: CRD42020218825. The search was performed in CINAHL, Medline, Scopus, and Web of Science up to January 2021. The PICOS recommendations were applied. The search was conducted by two reviewers, who completed the data extraction of included articles. Methodological quality was assessed using the STROBE checklist, and a meta-analysis was conducted. The literature search strategy identified 227 articles. Five studies remained and were included. Only three studies were included in the meta-analysis. Two articles used accelerometers to objectively compare PA levels before and during the pandemic. Three studies made this comparison using an online survey. All articles showed a decrease in PA levels during the COVID-19 pandemic. The meta-analysis showed a significant reduction in PA levels during pandemic. PA levels during the COVID-19 pandemic have been reduced with respect to previous levels of PA in patients with CD.