Query getting slow in mysql

I ran a mysql query :

SELECT count(*) FROM tab_master where dateA ='2015-10-10' group by RecA

The mysql table "tab_master" has a size around 5GB and above query execution time : 65.08 sec. (more than 2 mins) Is that going normally or taking slow. If it's taking slow, then I need some suggestion and tuning from you. Thank you.