This is a warning. If you are familiar enough with your backup strategy to know that this is not a problem that just ignore it, if not read further.
It is generally recommended that full backups be run regularly, and based on your business needs a full backup should be run often enough.
Once a day is a good recommendation, but this can change depending on your use of transaction log backups and differential backups.
Use the Backups Report to check on the status of all your backups.