Staying active means continuing with normal daily activities as much as possible, including going to work. It also means trying to reduce long periods of inactivity. No specific exercise(s) is needed at this stage.
People with low back pain who remain active, even when in pain, do better in the long term. In fact, it appears that the longer a person stays in bed because of low back pain, the worse their ability to work and/or return to work becomes.