up the pipe that is leaving the pump. The fact that it comes on and your basement isnt flooded tells me it is working. If you have had alot of rain lately there is probably alot of water in the ground.
The hole in the floor acts like a well and water collects in the hole. The pump has a switch that measures water level and at a certain height it switches on and pumps the water out. Some water is normal at the bottom of the hole so the pump doesnt suck air.
Watch it go through its cycle. If the pump comes on, pumps for a few minutes, shuts off and then water drains back into the hole from the pipe, then quickly turns itself on again, this may indicate the need for a (new) check valve.
If you are concerned, have it inspected. The pumps job is to keep you dry.