Do you have 32-bit Java?
& if it continues happening, click the arrow of the Java process that keeps spiking, and then see which program it says. If it's OSBot, right click it & switch to process or whatever, and it should pop up the client.
Do you know which client is the one that spiked to 20%?
& you'd be surprised, my video card starts shitting itself when I bot & play league at the same time, so that could quite possible be your issue.
Get a better computer / don't run so many things at once, since your computer can't handle it.
Edit:
& what script are you running?
Some scripts are more CPU demanding than other, and mirror has higher CPU usage by default as well.