Unfortunately this is not possible. Not even in the latest version of assystweb 11.5.3. See wiki information

https://wiki.axiossystems.com/assyst11-5Wiki/index.php/Overview_of_the_Use_of_Expressions_and_Filters_in_assyst#Visibility_Expressions

In 11.5 it should be possible to add a visibility expression to a custom group and place the system field in that group. Not a visibility expression directly on the system field but will do a similar job.  

Hi Amal, 

This is not currently possible directly on the field however as Alan has described it can be achieved using custom groups on the form. 

There’s an idea open for this functionality to be added in the ideas area, if it’s something you would be interested in please give it an up vote.