To dream that you are at work, indicates that you are experiencing some anxiety about a current project or task. The dream may also be telling you that you need to "get back to work". Perhaps you have been slacking and need to pick up the pace.
To dream that you are at your former or past work, suggests that there is an old lesson that you need to learn and apply to your current situation.
To dream that you are hard at work, signifies success and merit. Alternatively, it may suggest anxieties about a current task or project. You may need to "get back to work" and stop procrastinating.