Yes, we need to ask God to forgive us for our current sins. When we became Christians by confessing our sinfulness, accepting Jesus as our Savior, and then giving our entire heart and mind to follow God’s will, Jesus’ blood covered all of our sins. However, God does not miraculously make us perfect in our fallen flesh.
The Apostle Paul was a dedicated Christian. But in Romans 7:18-19, he confessed that even he could not live righteously. “For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right but not the ability to carry it out. For I do not do the good I want, but the evil I do not want is what I keep on doing.” (ESV) Later in verse 24, he recognized it was his sinful flesh (not his new creature) which constantly sinned. “Wretched man that I am! Who will deliver me from this body of death…with my flesh I serve the law of sin.”
The Apostle John also discussed the Christian’s struggle against sin. John was addressing Christians when he wrote, “If we say that we have no sin, we deceive ourselves…” 1 John 1:8. Then immediately in verse 9, he told us what to do when we do sin. “If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.” He further explained, “My little children, I am writing these things to you so that you may not sin. But if anyone does sin, we have an advocate with the Father, Jesus Christ the righteous.” (1 John 2:1)
The scriptures are full of heroes that modeled the practice of asking the Lord for forgiveness. Daniel did so in Daniel 9:20, “…while I was speaking, and praying, and confessing my sin…” Nehemiah wrote, “…I pray…and confess the sins …of Israel, which we have sinned against thee…”(Nehemiah 1:4-6). Both prayed for forgiveness and were also commissioned of the Lord to do great things!
Finally, Jesus taught us to ask forgiveness in the Lord’s Prayer in Matthew 6:12,”… forgive us for doing wrong, as we forgive others…” (CEV).
In summary: Christians will continue to fight against the sin in our fallen bodies. It is only after death, when we are given a perfect, sinless body, that we will sin no more. Until then, we need to ask God for forgiveness whenever we sin.
"For I will be merciful to their unrighteousness, and their sins and their lawless deeds I will remember no more.” (Hebrews 8:12)