It's generally the last place men lose excess body fat. On top of doing some of the exercises in this forum, it's important to consider your diet. It was only after closely examining my diet that I got rid of what you call "fat on the lower back."
There is no way to target specific areas for fat loss. All you can do is exercise and function at a calorie deficit (eat less than you burn) and eventually your fat stores will dwindle. Lower-back fat and that slight softness on the belly are the "spare tire." Men's bodies are loathe to get rid of that spare tire more than anything else.