Yes, as a matter of fact butter could go bad. When talking about salted and unsalted butter, unsalted butter tends to go bad easily than salted butter because the salt in a salted butter helps preserve the butter. Unsalted butter goes bad if left at room temperature for 6 hours, while salted butter can last for a few days when placed at room temperature. However when placed inside the fridge, unsalted butter can last for more than a month, while salted butter on the other hand lasts for months.