Generally speaking, no; you can only access the content on Bible Gateway when you’re online.
That said, there are a few ways to access particular Bibles offline. Our mobile app allows for certain (although not all) Bibles to be accessed offline in the app. And some of the Bibles in our library are available as downloadable PDFs direct from their publisher. You can see a list of such downloadable Bibles at the Available Versions page.