My oscilloscope picks up 600kHz sine wave signal when connected to an open wire
There's nothing to "fix".  You are connecting your scope probe to an antenna, and the scope is displaying a resulting signal.  If you didn't see it, that would mean your scope is brokent.  I suppose you might wonder if you are really viewing a 600kHz sine, or an aliasing of a higher frequency, but that's a different issue.

If you want to not see such a signal, hook your oscilloscope up to something you actually want to measure.