Is the z score corresponding to a number or score below the mean always negative?

Yes

Step-by-step explanation:

The z-score corresponding to a number or score can be calculated using:

Where x stands for the individual scores, and

stands for the mean.

Since

for all numbers or scores below the mean, the difference will always be negative these values below the mean.

This will always result in a negative z-score for all numbers below the mean.