You should not ask this question once in a while. In fact, you should not even ask it once. When you pose a question like this, you are essentially admitting that it would not be unreasonable for your manager to fire you. This means that asking this question can actually increase the likelihood that you will be terminated.
Besides, asking this question has not eased your mind at all. If the question really did what it is supposed to do, you would only need to ask it once and then your insecurity would disappear. Obviously, if you are asking it more than once, it is not easing your anxiety.
Then there is the question of what your manager's answer actually means. If he says, "no," you do not believe him. If you believed him, you would not feel a need to ask him again and again. And he is not likely to answer with, "yes." If he is going to terminate you, he will call you into his office and do so. He is not likely to respond by saying, "Well, as long as you mention it, yes, you're fired."
You should listen to your friends and focus on getting fired up rather than getting fired.
| 
