If I had an average Bachelor degree and a year of working experience can I apply for a Master's Program?
You will probably need to take the GRE and get a solid score. It also depends how you did in particular courses. E.g. did you bomb all the hard classes and ace a bunch of easy ones to pass overall? In grad school they may all be hard classes. Not to discourage you too much though. If you apply far and wide you may be able to get in somewhere with just about any background. 

The concern of the school admissions is not just some competitive cutoff for merit, but that you will fail out and waste your time and money. There are definitely benefits of working, and it will help you. Especially if you get a job that uses some of the skills you need for your Master's program, like programming. If you can get a job precisely in "Data science" it may help significantly.