A covalent bond is a bond where the two elements being bonded SHARE electrons that make the bond. So, if the bond is made by a sharing of electrons, then it is considered a covalent bond.
Ammonia has the formula of NH3. It can be formed many ways, but commercially it is formed by something called the Haber process. This combines hydrogen gas (H2) and nitrogen gas (N2) in the ratio of of 3:1. It looks like this:
3H2 + N2 ==> 2NH3