Illuminated Light Switch flickers
If it is an old switch that is internally illuminated when off, then it probably uses a small neon bulb as the light source.  They do burn out eventually.  Usually they flicker before they completely burn out.

The neon lamp burning out is not hazardous in any way.  The lamps are not replaceable.  If you want to fix it then you will need to replace the old illuminated switch with a new one.