• Average of total rows (from column 2, for example):

awk -F';' '{ tot += $2; row++ } END { print tot/row }' file.csv

• Average of total columns:

awk -F';' '{ tot=0; for (c=1; c<=NF; c++) tot+=$c; aver=tot/NF; print $0 ";" aver}' file.csv