Obviously, the switch is failing. The only real danger is that it could produce a poor connection when on and and cause heating within the switch; this is a low probability and I really wouldn't worry about it.
the larger probability is that the switch will fail and you won't the able to turn the light on or off. To avoid running into that issue at an inconvenient time (e.g. it's dark and you cannot turn on the light), I'd go ahead and replace the switch now.
I'm going to make an assumption that you're inexperienced in this, If you want help changing the switch, turn off the circuit at the breaker and unscrew the cover and switch and pull it out of the box without disconnecting any wires. Take some photos and add them to this question. You may see that the wiring is simple enough that you feel confident in doing it yourself immediately. Otherwise, we can help you.