afni.nimh.nih.gov

You should be able to do what you want with any of these commands:

3dcalc -a epi_r1+orig -b a+i -c a-i -d a+j -e a-j -f a+k -g a-k -expr '(a+b+c+d+e+f+g)/7' -prefix epi_localmean

3dLocalstat -prefix epi_lsmean -stat mean -input epi_r1+orig.

3dmerge -dxyz=1 -1filter_mean 1 -doall -prefix epi_mrgmean epi_r1+orig