  We demonstrate high fidelity single-qubit gate operation in a trapped single
neutral atom. The atom is trapped in the recently invented magic-intensity
optical dipole trap (MI-ODT) with more stable magnetic field. The MI-ODT
efficiently mitigates the detrimental effects of light shifts thus sufficiently
improves the performance of single qubit-gates. The gates are driven with
microwave, and the fidelity of gate operation is characterized by using the
randomized benchmarking method. We obtain an average error per Clifford gate of
$3.0(7)\times10^{-5}$ which is much below the error threshold ($10^{-4}$) for
fault-tolerance. This error is found to be dominated by qubit dephasing, and
the corresponding coherence time relevant to the Clifford gates is also
measured experimentally. This work is an essential step toward the construction
of a scalable quantum computer with neutral atoms trapped in an MI-ODT array.
