Yes Kleptomania is a mental illness and treatment through mental health therapy can help the person who has Kleptomania.
However Kleptomania cannot be fully cured but treatment and therapy can help curb the urge to take things.
Although Kleptomania is a mental health illness it will not stop you from being arrested, go to jail, prison etc when you're caught stealing things.
So if you have Kleptomania you should seek treatment to try and stop the urge to steal.
The Kleptomania mental illness is the recurrent inability to resist urges to steal items that you generally don't really need and that usually have little value.
It can get you into trouble with the law so you need treatment.