Yes, miracles are supernatural; miracle can be defined as an event that happened as a result of supernatural power and not by any scientific law or natural law. All the miracle that happens is credited to a supernatural being or a person that is superior to the human race.
There are different causes of sickness we see today, and later on, they are gone even after the physician has confirmed that they have a few years on earth to life. For example, an HIV patient can test negative after testing positive.
Another example is a patient that is in stage four cancer, and after when a miracle occurred, the deadly cancer cells disappeared from the body. Lastly, all miracles are said to be supernatural.