I would list the title of the thesis along with an expected completion date.
Depending on the format of your CV, this may just be the year, or, if you know the exact deadline, the date in Month, Year or DD/MM/YY format (the specifics of your long date formatting is country-dependent of course).
The listing on the CV might look something like
Bachelors' Thesis: "My Awesome Thesis Title Goes Here." May 2017
"My Awesome Thesis Title Goes Here." (Bachelors' Thesis, expected
completion date 30/05/17)
If you are submitting some form of covering letter as part of your application, it would also be a good idea to talk about your thesis there and also note that it is not yet complete. However, I think the admissions committee would be aware that if you are a current undergraduate student that your thesis is likely to be unfinished at this point. Good luck with your application!