Mice are naturally living in our suburbs and regional areas so it is likely that you will see one in your yard at some point. Seeing one mouse is not a problem but they may be just one of a large population that can find a home in your yard. If you see more than 1 then it may be time to take action to deter mice from your garden. Mice can breed quickly so two mice can quickly turn into a swarm in a few weeks. Natural traps should be your last resort but work on deterring them first and cleaning up your yard to reduce the space for them to live.