Yes there were explosive devices on the beaches and in the hinterland.

The most famous is maybe the so called "Rommelspargel" (Rommels asparagus). These were wooden sticks or poles (~5 meters long) that were dug into the ground of beaches and of fields in the hinterland. Some of those carried mines or grenades triggered with tripwires, others were pointed. Their job was to destroy allied boats (they were dug in so they were just under the surface on high tide) and on the fields to stop paratroopers and gliders. Their effectiveness was limited though, since the allied knew about them and avoided them as well as they could.

But this were not the only mines placed. Rommel (as the coordinator of the defense in France) was sure that the German forces need to stop an invasion in short time close to the coastline if they were to have a chance (and he was right: The superiority in manpower and industrial output would and did mean certain defeat as soon as the allied could bring supplies and reinforcements to France safely). To achieve this he placed his forces close to the coast in strongholds. Between those strongholds extensive mine fields (both anti personell and anti tanks) were places to stop the allied forces from gaining a wide foothold.

To my knowledge no land mines were dug in at the beaches, as they wouldn't have any impact on high tide (the Germans expected a landing on high tide, even though they were prepared for low tide landings as well) and would be prone to be washed away due to the surf.

Sources:

Dieter Ose: Entscheidung im Westen 1944. Der Oberbefehlshaber West und die Abwehr der alliierten Invasion

Hans Wegmüller: Die Abwehr der Invasion. Die Konzeption des Oberbefehlshabers West 1940–1944