Mindfulness-based interventions (MBI) are a recognized effective psychological practice characterized by attention control, awareness, acceptance, non-reactivity, and non-judgmental thinking obtained through the practice of meditation. They have been shown to be useful in reducing stress and enhancing well-being in different contexts. In this research, the effectiveness of an MBI was evaluated on variables that can promote successful job performance such as mindfulness trait, positive and negative affect, forgiveness, personality strengths and satisfaction with life. The intervention was carried out through a smartphone application called “Aire Fresco” (Fresh Air) during 14 days in the middle of the quarantine produced by the Covid-19 pandemic. The study sample was composed of 164 Spanish people who were distributed in two groups: control group and experimental group, which were evaluated before and after the intervention. The MANCOVA performed showed an overall positive effect of the intervention on the variables evaluated. The different ANCOVAs carried out showed that the intervention was beneficial in increasing mindfulness trait, reducing negative affect or increasing life satisfaction, among others. Our study is, as far as we know, the first to demonstrate the effectiveness of a brief intervention in mindfulness conducted using a smartphone application in Spanish.