Windows process CPU Utilization and Memory Utilization

In general, when a process is very actively doing it works, does it CPU utilization and memory utilization increase?

This is because when i try to keep track of the CPU utilization and memory utilization of my FTP server process (ftpserver.exe), the CPU utilization increase, but the memory utilization decrease. Why is this happening?

PS:
CPU Utilization is taken from Process\% Processor Time
Memory Utilization is taken from Process\Working Set (I want to measure the physical memory it uses)

Any help is appreciated. Thanks.