If you have one mouse in your house then there is likely other rats and you likely have a mouse infestation or soon will have a mouse infestation.
Mice can be in your attic, under your house or even in your walls and you may not even notice them.
If you do see one mouse in your house you should set out multiple mouse traps to catch the mice just in case their is more than one mouse in the house.
Once one mouse gets into your house and finds food then other mice will soon follow so you need to get rid of that mouse and any other potential mice before the infestation gets too bad.
You can also set out glue traps for mice or use the snap traps or if you need too set out some mouse poison.
The mouse poison can take 5 days to fully kill the mouse so I would use mouse traps and try to trap them first.