Purpose: This study aimed to evaluate the effect of mHealth-based mindfulness intervention on trait mindfulness, stress, anxiety, and depression among Registered Nurses caring for patients with COVID-19 in Jordan. Method: Using a pretest-posttest parallel controlled design, 102 nurses from the King Abdullah University Hospital were randomly assigned into experimental (n = 51) and control (n = 51) groups. The experimental group received 5 weeks of individual 30-min mindfulness intervention sessions via WhatsApp. The collected data included demographic information as well as baseline and postintervention scores from the Mindfulness Attention Awareness Scale and the Depression, Anxiety, and Stress Scale. Findings: Paired t-tests revealed that the experimental group demonstrated significantly lower levels of stress, anxiety, and depression, as well as higher trait mindfulness scores following the intervention. Independent t-tests indicated that, compared to the control group, the experimental group had significantly reduced depression and stress levels and increased trait mindfulness scores at the end of the intervention. Although anxiety scores were lower in the experimental group following the intervention, the difference between the groups was not statistically significant. Conclusion: This finding aligns with existing literature, which has reported similar outcomes in studies on mindfulness interventions. These studies highlight the potential of mHealth-based mindfulness intervention as a holistic approach to enhancing psychological well-being among nurses who care for patients with COVID-19. Trial Registration: Clinicaltrials.gov; ID: NCT06401252.