Acts 7:55-56 (NKJV)
But he, being full of the Holy Spirit, gazed into heaven and saw the glory of God, and Jesus standing at the right hand of God, and said, "Look! I see the heavens opened and the Son of Man standing at the right hand of God!"
Hebrews 1:3 (NKJV)
who being the brightness of His glory and the express image of His person, and upholding all things by the word of His power, when He had by Himself purged our sins, sat down at the right hand of the Majesty on high,
When Stephen was preaching, he made the Pharisees so mad that they stoned him to death. He was the first Christian martyr. Stephen was ready however. He was full of the Spirit and when he looked up to heaven he saw Jesus standing there. Now in Hebrews we know that Jesus has finished the work he was sent to do, dying on the cross for our sins, and is now seated at the right hand of the throne of God. From this, I can only conclude that upon seeing the love and dedication of Stephen for his Lord, that Jesus stood up in approval to welcome Stephen into heaven.