You can determine the status of the fulltext indexing by querying the indexing properties like this:
SELECT FULLTEXTCATALOGPROPERTY('IndexingCatalog', 'PopulateStatus') AS Status
Populate Status:
0 = Idle
1 = Full population in progress
2 = Paused
3 = Throttled
4 = Recovering
5 = Shutdown
6 = Incremental population in progress
7 = Building index
8 = Disk is full. Paused.
9 = Change tracking
But also pay attention to this note in the article:
The following properties will be removed in a future release of SQL
Server: LogSize and PopulateStatus. Avoid using these properties in
new development work, and plan to modify applications that currently
use any of them.
EDIT: Corrected link to a newer page and added quote from the note