No, when you login to the software for the first time it requires a network connection to provide you an activation token securely from the DesignSpark server.
Thereafter, every 30 days a validation of this activation token is required.
Going online also allows the software to update any help documentation and the start page content - which provides quick links to design projects and support forums.
If you often work remotely and don't have a stable network, you can still use the software but try to find a way to connect once a month to keep DSM activated.
If you are at a workplace and have trouble activating the software, see here: https://designspark.zendesk.com/hc/en-us/articles/213291329