How often should I change the air filter on my lawn mower?

It is a Honda mower and runs well now that I changed the spark plug. Should I change the air filter as well?
How often should I change the air filter on my lawn mower?
and oil
How often should I change the air filter on my lawn mower?
Is it a sponge type or paper filter?
i change mine once a year along with the oil and plug.
If it is a sponge type , wash it in soapy water , squeeze it dry and apply just enough clean engine oil to soak it lightly , it's the oil that dust clings to. A sponge type will last for years if properly maintained. If it is a paper type you can blow it out with an air hose a couple times usually before you have to replace it. Try not to get a paper type wet as they tend to come apart and may get pieces sucked into the carburetor.
Honda recommends checking the air filter element before each use and servicing it at least every 50 hours. More often if used in dirty/dusty conditions. Your machine has a foam filter element that is easy to tell when it's dirty and you can wash with solvent or soap and warm water, rinse and dry, then soak it in clean engine oil. Wring the excess oil out and reinstall. A foam element can last for years if it's kept clean.