Sparks appear when pluggin in USB

[aflumbahgee]

When I'm plugging in a USB into the back of the my computer into the motherboard I see little blue sparks just before its plugged in...Is this bad? How do I fix it? It happens when I plug stuff into my extension lead as well :/

I have another unrelated question, is it ok to hoover the dust off your PC while its still on? Like the back where there is a dust build up and on the front intake? Or does it build up static?

 

[Swordkd]

Sparks are bad, period.

Vacuuming the back of the case, or the front intake grill while it's running is not.

 

[aflumbahgee]

How do I stop the sparks?