Denying the Antecedent is where the conclusion of two statements is thought to falsify the initial truth statement. For this to happen we need an initial statement  of truth. Then we make a second statement about the initial statement that is also true. From this if we conclude that the initial statement is false we have denied the antecedent, thus committing the fallacy.

Denying the Antecedent Example

If Mike is a Muslim then he is also a human being.

Mike is not a Muslim

Therefore Mike is not a human being.

Logic Structure

If A then B

A is not true

Therefore B is not true