When I see a moving meter I check to see how many gallons per hour based on a 20 to 30 minute timeframe. When I enter the house it usually turns out the homeowner has the dishwasher running, the ice maker has filled once or there is a toilet valve leaking. It could also be a dripping faucet inside or out.
Pull the meter lid and mark the dial and check again in 30 minutes after checking all of the above. The big bad news is it could be a plumbing leak under the slab. It happens but the other little things are a higher probability.