I want to keep t1,t2 and drop all other tables.
You can use information_schema to find table names, and even format the results as a bunch of DROP statements.
SELECT CONCAT('DROP TABLE ', TABLE_NAME, '; ')
FROM information_schema.tables
WHERE table_schema = DATABASE() AND table_name NOT IN ('foo', 'bar', 'baz');
(The DATABASE() function returns the currently use'd database.)
Using PREPARE and EXECUTE, you could even avoid copy & paste, and (in MySQL 5.0.13 and later) write a stored procedure to do this.