The coronavirus disease 2019 (COVID-19) pandemic has resulted in significant lifestyle changes due to shelter-in-place confinement orders. The study’s purpose was to assess if the COVID-19 pandemic affected self-reported diabetes prevention behaviors among American adults with prediabetes. As part of a randomized clinical trial among adults with prediabetes and overweight/obesity, questions were added to existing study surveys to assess the effect of the COVID-19 pandemic on diabetes prevention behaviors and stress. Survey responses were summarized using frequencies. 259 study participants completed seven COVID-19 survey questions from June 2020 to June 2021. Participants were 62.9% female, 42.5% White, 31.3% Black, 11.6% Asian, 8.1% Hispanic, and 6.6% Other. Over 75% of participants reported that the COVID-19 pandemic affected physical activity levels, with 82.1% of those affected reporting decreased physical activity; 70.3% reported that the pandemic affected their eating habits, with 61.7% of those affected reporting their eating habits became less healthy; 73.7% reported that the pandemic affected their level of stress, with 97.4% of those affected reporting that their level of stress had increased; 60% reported that the pandemic affected their motivation to adopt/maintain healthy habits, with 72.9% of those affected reporting their motivation decreased. A high percentage of study participants with prediabetes reported decreases in health promotion behaviors and increases in stress due to the COVID-19 pandemic. Consequently, the pandemic could lead to increased diabetes incidence. Strategies to improve diabetes prevention behaviors and address mental health concerns among those at-risk for diabetes are critical during and after the COVID-19 pandemic.