The results of hundreds of studies show that exercise has a slight protective effect against back pain for the general population. This doesn't mean you can't injure yourself or overdo it and end up with back pain.
Even in these cases, exercise is often the best treatment. There's no proof that exercise increases your risk of back pain. Regular exercise even when you have back pain is safe. Scientists think exercising will reduce your risk for future back problems. Some studies show workers who exercise take fewer sick days.
Research also shows fewer reinjuries and sick days taken by workers with back pain who continue to exercise regularly. Your best bet is to get back to an exercise program slowly and build back up to your previous level.