We tested whether the tendency to worry could affect psychological responses to quarantine by capitalizing on the opportunity of having collected data before the COVID-19 outbreak on measures of worry, anxiety, and trait mindfulness in a group of university students. Twenty-five participants completed self-report measures assessing worry (Penn State Worry Questionnaire, PSWQ), anxiety (Anxiety Sensitivity Index, ASI-3), and trait mindfulness (Mindful Attention Awareness Scale, MAAS) at T0 (pre-lockdown, 4 November 2019–17 February 2020) and T1 (at the end of lockdown, 26 April–30 April 2020). We compared assessments at the two time points in the whole sample and in high and low worriers (defined at T0 by scores on PSWQ respectively above and below 1.5 SD from mean of the Italian normative sample). High worriers showed at T1 a significant increase of anxiety sensitivity and fear of mental health in comparison to low worriers. Moreover, in the whole sample, at T1 trait mindfulness was inversely related to worry and fear of mental health. A valuable approach to support individuals experiencing anxiety related to the COVID-19 outbreak could be represented by mindfulness-based interventions improving the ability to focus attention and awareness on the present moment.