Abram believed the LORD, and he credited it to him as righteousness.  Genesis 15:6

Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.  Mark 16:16

Many characters in the Bible believed.  Noah, David, Nehemiah, Paul, Peter, John.  Was it the same type of belief?

The goal of belief is to receive the credit of righteousness.  You have to believe so correctly, so humbly, so reverently that God looks at you as clean of any sin.  Your belief must qualify you for the removal of sin.  It worked for Abram and it worked for New Testament believers.

Your belief must put you into a relationship with God.  You reach a different status because of your belief.  It goes beyond information and understanding ("I know of God" or "I go to church and hear about God"), but moves closer to intimacy and reliance ("I love God" or "I trust God").

That's the same in both Testaments.

However, the information people from both Testaments believed in was different.

Old Testament believers knew of God, his plan to create a nation, his care for the Jewish people, his power to make things happen, his power to create miracles and the promise of one who would come in the future to save them (a Messiah).

New Testament believers knew of God his Father, Jesus his Son and the Holy Spirit.  They knew of Jesus living, dying and resurrecting, his promise to redeem us from our sins and the gathering of all believers in heaven.

With both types of beliefs, Old and New, the believer could just know God or trust God.  They could understand God or love God.  God desired that closeness that sought after his heart, not just gathered more information about him.