O2 Sensor question

This is probably a dumb question, however, is it dangerous to drive around with a bad o2 sensor? I was told at my local garage that was why my check engine light was on. I dont have the money to fix it atm and was wondering if it was okay to drive around with it as is till I do.

the only thing it could be dangerous to is the environment

and if its your 2nd O2 sensor, it could be bad to your cat by basicly burning the inside up and leading to being bad to the enviroment.