Two weeks ago one of my emails was replied by a professor who expressed his interests in my work and consider me as a potential postdoc. He told me that he is going to apply for funding then will inform me. At this moment, I do not know whether I keep sending emails to other professors for postdoc position or wait for email from potential mentor?
I recommend that you keep all your options open up until you have something firm. There are too many things that could go wrong for you to make assumptions that you "have" a position. Interest was expressed. Action was promised. A contract was not offered.
Don't mislead people, of course, but don't drop your other efforts.