No biographical details are currently known (Google searches bring up an Argentinian singer named Mario Bustos, but this is not the same person).
With several uncredited roles and gaps in the early 50's and late 60's where his filmography is rather sparse, it would seem likely that there could be undocumented roles to be found.
- Sabela de Cambados .... Ernesto Mirandas (credited)
1952 - El sistema Pelegrín .... Señor Pons (credited as "Mario Bustos")
- Persecución en Madrid .... Don Ernesto (uncredited)
1955 - El golfo que vio una estrella .... Post Office manager (credited)
- Lo que nunca muere .... Colonel (credited as "Francisco Mario de Bustos")
1956 - Heredero en apuros .... Theatre manager (credited)
- La legión del silencio .... Bus driver (uncredited)
- Sucedió en mi aldea .... Detective (uncredited)
- Veraneo en España …. (credited, but not found - scenes deleted)
1957 - El último cuplé .... Don Tomás (credited as "Francisco Bustos")
- La cárcel de cristal .... Santos (credited)
- La estrella del rey .... Minister for culture (credited)
- Un tesoro en el cielo .... Office manager (credited)
1958 - Historias de la feria .... Victim of attempted robbery (credit unknown)
1959 - El frente infinito .... Captain Campos (credited)
- Las aventuras de Taxi Key .... Señor Visconti (credited)
1960 - Alfonso XII y María Cristina ¿Dónde vas triste de tí? .... Doctor (credited as "Mario Bustos")
- Altas variedades .... Promoter (credited)
- Amor bajo cero .... Ski lift operator (credited as "Mario Bustos")
- Gaudí .... Cosculluela (credited as "Francisco M. de Bustos")
1961 - Hay alguien detrás de la puerta .... Impresario (credited as "Mario Bustos")
- Los dos golfillos .... Restaurant owner (credited as "Mario Bustos")
- Placido .... Don Rodolfo (credited)
1962 - Bahía de Palma .... Señor Castillo (credited)
- El amor de los amores .... Minister (credited)
1963 - El precio de un asesino .... Don Silverio (credited)
- Los farsantes .... Ramón (credited)
1964 - Crimen .... Relo (credited)
- La barca sin pescador .... Bank manager (credited)
1967 - Romeo y Julieta (TV movie) .... Priest (credited as "Mario Bustos")
1972 - El estudiante de Salamanca (TV mini-series) Eps. 2, 5 .... Doctor (credited as "Mario Bustos")
- El presidio (1954) EdCE
- La canción del penal (1954) IMDb
- Sor Angélica (1954) IMDb
- Sitiados en la ciudad (1957) IMDb
- El ángel está en la cumbre (1958) IMDb as Club president
- José María (1963) IMDb as Sr. Marqués
- Adiós, Priscila (1964 TV movie) Novela series. IMDb
- Le voleur de Tibidabo (1965) EdCE
- ¿No te has muerto aun? (1970 TV series or TV movie?) IMDb has this title listed twice, as an episode of the series "Sospecha" and as an episode of the series "Hora once"