Algunos patrones de conducta aumentan el riesgo de trastornos físicos y mentales. Fomentar hábitos saludables, como la actividad física (AF), es clave en la promoción de la salud, sin embargo, lograr la adherencia a un estilo de vida activo sigue siendo un desafío. Este estudio presenta los efectos del programa MAFyS, una intervención grupal virtual dirigida a adultos para promover la motivación hacia la AF. Participaron 32 adultos argentinos (M = 38.56 años, DE = 12.0), comparados con un grupo control (n = 18) que recibió información psicoeducativa pero no participó de la intervención. Se realizaron evaluaciones pre, post intervención y a los 3 meses de seguimiento, utilizando el IPAQ y un podómetro móvil (pasos/semana). Se hallaron diferencias estadísticamente significativas en el nivel de AF entre los grupos, tanto post intervención (METs: U = 201, p = .018, r = –.396) como en el seguimiento (METs: U = 139, p = .003, r = .519; pasos/semana: U = 157, p = .007, r = .455), a favor del grupo experimental. También se observó una reducción del sedentarismo (U = 147, p = .004, r = .490). Los resultados sugieren que esta intervención es eficaz para aumentar la AF y reducir el sedentarismo, con efectos sostenidos a mediano plazo. Palabras clave Intervención virtual - Actividad física - Sedentarismo - Motivación - Promoción de la salud ABSTRACT VIRTUAL MOTIVATIONAL INTERVENTION: INCREASING PHYSICAL ACTIVITY AND REDUCING SEDENTARY BEHAVIOR Certain behavioral patterns increase the risk of physical and mental disorders, making the promotion of healthy habits—such as physical activity (PA)—a key strategy in health promotion. However, achieving adherence to an active lifestyle remains a challenge. This study presents the effects of the MAFyS program, a virtual group intervention aimed at enhancing motivation for PA in adults. Thirty-two Argentine adults (M = 38.56 years, SD = 12.0) participated and were compared to a control group (n = 18) that received psychoeducational information but did not take part in the intervention.Assessments were conducted pre- and post-intervention and at a 3-month follow-up, using the IPAQ and a mobile pedometer app (steps/week). Statistically significant differences were found in PA levels between groups, both post-intervention (METs: U = 201, p = .018, r = –.396) and at follow-up (METs: U = 139, p = .003, r = .519; steps/week: U = 157, p = .007, r = .455), favoring the experimental group. A reduction in sedentary behavior was also observed (U = 147, p = .004, r = .490). These findings suggest that the intervention is effective in increasing PA and reducing sedentary behavior in healthy adults, with sustained effects in the medium term. Keywords Virtual intervention - Physical activity - Sedentary behavior -