A httpd process is required per web server request. If needed (not enough processes are already running), a new processed is spawned to fulfill a new request. The # of processes doesn't equal # of visitors.
most of the time the CPU use is between 1% and 4%, but i noticed this morning one httpd process at 18%. should i be alarmed?
Probably nothing to worry about. Try seeing if that httpd process has children. Often httpd processes with higher CPU usage spawned child processes to execute a script or what have you.
Do something like :
look for the httpd process with the higher CPU usage and see if it has child processes and if so, check what they are/do.