LEDs in household outlet
Yes, such indicators often do flicker. Try sweeping your vision across it rapidly. You'll likely see a series of dots.

For example, here's an outlet in my kitchen:



And here's a picture of it taken with deliberate motion blur:



The flicker actually bothers me when I walk through the dark kitchen at night, in the same way that the PWM taillights on moderns cars do when driving at night.