We have studied the dependence of the high frequency QPO ( \sim 284 Hz ) on the phase of the low frequency QPO ( \sim 6 Hz ) in the black hole X-ray binary XTE J1550-564 in the observations of the Rossi X-ray Timing Explorer ( RXTE ) performed on MJD 51241 .
By selecting the local maxima and the local minima in the light curve on the 6 Hz QPO time scale , we have found the corresponding high frequency QPO frequencies are consistent within 1.5 \sigma .
However , the average central QPO frequency of the maxima and the minima is about 2.0 \sigma lower than the average high frequency QPO frequency obtained in the entire observation .
This marginally suggests that the high frequency QPOs probably varies in frequency on short time scales .
We briefly discuss these results and their consequences .