ERROR: Compute used in variable between runs is not current

Hi,dear lammps users.
I would like to store per atom charge information and add the ones whose charge is blow -1.2 to one group. How could I realize it during the dynamic runs?
When I use commands below:

compute percharge oxygen property/atom q
compute h oxygen reduce sum c_percharge
thermo_style custom step temp c_h
group consume variable nq
vairable m equal count(consume)
ERROR: Compute used in variable between runs is not current (…/variable.cpp:1086) will appear. Could anyone help me out?

How and when is your atom-style variable nq evaluated?

Ray