Yes, of course it is! Scrum is a framework to help teams and organisations on their path to agility, but it is by no means the only way to be agile.
Back before I knew about Scrum, I worked on projects that were agile. Back then we didn’t really know what agility was all about, but that didn’t mean that it sometimes didn’t occur naturally. We just didn't make a conscious effort to be agile, as most organisations do nowadays.