Can I use my EMP Minefield to send an enemy ship back to its controller's dock before battle begins?

Yes. The rules state that once you have warped your ship into an enemy region, for the remainder of that management phase you cannot warp the ship again, activate its commands or use its abilities. So if you use EMP Minefield to send back an attacking ship, that ship still won't be able to warp again during that management phase, or so much as undock (since docking and undocking is considered a warp).