  We observed the Monoceros R2 molecular cloud with the ACIS-I array onboard
the Chandra X-ray Observatory. From the central 3.2' x 3.2' region, we detect
154 sources above the detection limit of ~5x10^-16 ergs s^-1 cm^-2 with a 100
ks-exposure. About 85% of the X-ray sources are identified with an infrared
counterpart, including four high mass stars in zero age main sequence (ZAMS)
and/or pre main sequence (PMS) phase. The X-ray spectra of the high mass ZAMS
and PMS stars are represented with a thin thermal plasma model of a temperature
above 2 keV. The X-rays are time-variable and exhibit rapid flares. These high
temperature plasma and flaring activity are similar to those seen in low mass
PMS stars and contrary to the behavior observed in high mass main sequence
stars. The X-ray luminosity increases as the intrinsic K-band flux increases.
However, the X-ray luminosity saturates at a level of ~10^31 ergs s^-1. We
conclude that high mass ZAMS and PMS emit X-rays, possibly due to the magnetic
activity like those of low mass stars.
