Is this heterocyclic boron molecule aromatic?
That molecule is indeed aromatic.

It satisfies Huckel's rule ($4n+2$) with $n=0$. It's also planar.

Lastly, the boron atom has three electron domains, meaning it can exist with $sp^2$ hybridization. The left-over p-orbital, whilst not actively forming $\pi$  bonds, can still complete a stable $\pi$ molecular orbital.