when you running workflows, the system Account automatically included in the Sharepoint Workflow Groups but you were not added the system account in the groups. So for removing the system account in the workflow run the stsadm commands.
stsadm -o deleteuser -url -userlogin sharepoint\system -group groupname
Example:
stsadm.exe -o deleteuser -url http://aurramu.blogspot.com/ -userlogin sharepoint\system Account -group testworkflowowner
stsadm -o deleteuser -url
Example:
stsadm.exe -o deleteuser -url http://aurramu.blogspot.com/ -userlogin sharepoint\system Account -group testworkflowowner
