Write SQL query to solve given problem: Among the active employees, how many of them have a courtesy title of "Mr"?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(T1.BusinessEntityID) FROM Employee AS T1 INNER JOIN Person AS T2 ON T1.BusinessEntityID = T2.BusinessEntityID WHERE T1.CurrentFlag = 1 AND T2.Title = 'Mr.'