Something that is active is characterized by movement and action. That action might be a random or temporary movement, such as someone who is active and exercises only now and then, or something continuous, like an active strain of a virus.
Since the adjective active suggests activity, applying it to anything implies some sort of motion or action. A person might be physically active, not sitting around and doing nothing, or mentally active, working the mind. In language, we refer to "the active voice" as one in which the subject does the action, in contrast to the passive voice, a rather boring style where the subject is the receiver of the action. Even in writing, it’s better to be active!