  We present angle-resolved photoemission studies on the rare-earth hexaboride
YbB$_6$, which has recently been predicted to be a topological Kondo insulator.
Our data do not agree with the prediction and instead show that YbB$_6$
exhibits a novel topological insulator state in the absence of a Kondo
mechanism. We find that the Fermi level electronic structure of YbB$_6$ has
three 2D Dirac cone like surface states enclosing the Kramers' points, while
the f-orbital which would be relevant for the Kondo mechanism is $\sim1$ eV
below the Fermi level. Our first-principles calculation shows that the
topological state which we observe in YbB$_6$ is due to an inversion between Yb
$d$ and B $p$ bands. These experimental and theoretical results provide a new
approach for realizing novel correlated topological insulator states in
rare-earth materials.
