The story certainly has supernatural overtones, but everything that happens in it can be given natural and plausible explanations. The father wishes for two hundred pounds to pay off the mortgage on the family house. It happens that the son Herbert is killed the very next day by being mangled in one of the machines at his place of employment. The proprietors offer to pay the Whites the sum of two hundred pounds in compensation for their loss and bereavement. These are strange coincidences, but Herbert might have gotten killed on that particular day because he stayed up late talking to their visitor and probably drinking more than he was accustomed to. That could make him lethargic the next day and more likely to be caught by the machinery. The fact that the company offered the father and mother the exact sum wished for could be a pure coincidence. Mr. White wished for a modest sum, and the company only wanted to pay a token amount of compensation. If Mr. White had wished for a million pounds and had somehow received it after his son's death, that would be a different story entirely.
When White's wife gets him to wish for his son to come back to life and return home, they hear a prolonged knocking at the door. The reader has been beguiled into thinking that this must be the horribly mangled Herbert White brought back in answer to the second wish. However, this could be just another coincidence. The person knocking so persistently might have been some motorist who needed assistance or directions. Mr. White uses his last wish to make the knocker go away, but that person would have to get tried of knocking anyway and leave of his own accord.
The fact that the Whites never know the truth for sure is what makes "The Monkey's Paw" so uncanny.