Yes, you can freeze fresh basil leaves and use them later. You can blanch whole leaves in boiling water or puree the leaves in a food processor with olive oil.
To blanch the leaves, boil a pot of water and throw clean basil leaves in it for 8-10 seconds. Immediately plunge the leaves into a bowl of ice water to stop the blanching. Allow to fully dry before storing them in a freezer-safe container. To puree the basil leaves in a food processor, use one cup of basil leaves and one tablespoon of olive oil. Once combined, use an ice cube tray to freeze into cubes.