Presumably, you have this relationship:
Clients::ClientID = Users::ClientID
You can create a second table occurrence of Users (click the box in the relationship graph and then click the button with two plus signs.)
Create a calculation field, cActive, in Clients that always returns a status of "Active"
Now make a second relationship:
Clients::ClientID = ActiveUsers::ClientID AND
Clients::cActive = ActiveUsers::Status
(ActiveUsers is the second table occurrence of Users)
A calculation field in Clients defined as Count ( ActiveUsers::ClientID ) will now return the number of Active users for the current client record.
Your title says, "Total Number of Fields." What you are really asking, though, is a sum of related records. Phil has outlined how to achieve this with a relationship. However, I would start thinking about using flag fields. For a user that is "Active", create a field that is a number, "flag_Active" and format this field to be a checkbox with a value list of "1". Resize this field on the layout to just show the checkbox.
In Clients, create a calc field, result number, zz_Constant1 =1. To get a count of how many active users a client has related to them:
Clients::ClientID = Users::ClientID AND
Clients::zz_Constant1 = Users::flag_Active
Using flag fields scales well, because you can use the same zz_Constant to filter many relationships from Client.