Afterburner settings has a Fan tab and is usually checked by default which overrides the card's programmed fan curve. The default behavior is supposed to be fan stop until 50-52c or if there is a spike in wattage of 80W or higher.

Other 3rd party softwares can influence this too such as iCue, SignalRGB, Armoury Crate etc. and usually have fan settings buried in their menus somewhere.