VBA if active cell blank than msgbox to remind

are looking something like this

Are you trying to notify the user that the previous active cell is blank? Because hitting Tab or Enter will change which cell is the active cell. There is nothing built into VBA to tell you what cell was active before they hit Tab or Enter. You would have to build code that keeps track of which cell was active every time the user changes cells. Certainly feasible, but I would want to have your actual file to provide any further detail.

If I am guessing your intent correctly, then you have two other options that I can think of:

1. When the user thinks they are finished entering all data, they press a Submit button and at that point you scan for blank cells, rather than catching it at the moment it happens. This has the advantage of giving the user a little slack if they go to a cell, then decide to leave it blank so they can come back to it later after entering other data.
2. Use a UserForm instead, which has events that can detect if the user leaves a field