You might want to do a search as this topic has been brought up before.

As to your question, the first thing that should be mentioned that there was really no alliance between Germany and the USSR. It was more a "we will each deal with our own problems first and divide Europe into respective spheres of interest, and not worry about one another for the time being" sort of thing. It was never meant to be permanent or long term, just a way for both sides to buy time.

Now, the idea that the USSR was about to attack Germany was advanced by a popular Soviet (now British) author, however his work has largely been discredited or not even taken seriously in the first place, and is now viewed as revisionist history. The truth is that the USSR was just not ready for war in 1941. The Red Army was in the midst of a large reorganization and modernization program that wouldn't be complete until 1942 at earliest (but more likely even later than that). So whatever Stalin might have been thinking, attacking Germany before the Soviet Union was ready would have been a very foolish and reckless thing to do. The evidence we have suggests that Stalin was trying to buy time and not antagonize Germany at least for the time being.

The circumstancial evidence are strong that the soviet union planned to be at war with Germany ( not neccessarily as the attacking party ) in the near future but its very unlikely that they planned to attack in 1941. The other post talks about one specific historian, i guess he is talking about Suvorov. His theories are pretty speculative but at least on the basis bring up some interesting thoughts which he then uses to get to the wrong conclusion. The soviet army was not able to wage an offensive war in 1941 at least not against the Wehrmacht. Keep in mind Germany in 1941 had conquered western Europe. Nobody knows if Stalin planned to attack Germany since a lot of documents are still classified. Destroying documents was easy for Stalin so even the archives will not bring a definitive answer.

Some points which are brought up by historians who think Russia wanted to strike first. The most convincing ones:

The Red Army was positioned in a way which could be considered offensive. Airfields and support facilities where positioned very near to the front. That doesn't sound weird at first but normally you don't want all your aircraft directly at the front since you make yourself vunerable to advancing enemy troops and enemy bombers/attack aircraft. The reason you position your air fleet that close to the front is so that your aircraft can support your advancing troops when they are already in enemy territory. As Barbarrosa has shown the positioning was very bad in a defensive situation. A big part of the red airforce was destroyed in the first week. A counter argument here is that the russian operational doctrine requires immediate counter attacks deep into the enemy territory. This is true, that was the prevalent Russian strategy even today this concept is used. But if you expect to be reactive you likely don't use so much ressources next to the front, especially if you are Russia which can allow to lose some miles of land. But all this is speculative and no conclusion can be drawn with certainty.