Using your oven's self-cleaning cycle is a great way to clean your oven without the harmful fumes of oven cleaners. During the self-cleaning cycle, the oven heats up to an extremely high temperature and becomes hot enough to turn the burnt on food within your oven into ash. As a safety mechanism, the oven locks when it is in this mode because opening the oven when it is at such a high temperature could be dangerous. Sometimes, however, you may need to open the oven (for instance, if you find out you have left something in there accidentally) during its self-cleaning cycle.
Turn the self-cleaning feature off to interrupt it. If your oven has this feature, you will be able to stop the self-cleaning cycle but the oven may remained locked until it reaches a cooler, safer temperature.
If your oven can not be turned off during the self-cleaning cycle, turn your oven off at the breaker box or unplug it. It is likely that your oven will remain locked, but at least it will be turned off and not continue getting hotter.
If you have turned off your oven's self-cleaning feature because there is something in the oven, keep your eye on it until your oven reaches a safe temperature to assure you do not have an oven fire.