Sure it is. The first disciples believed in the divinity of the father and the son. History and any good Catholic will tell you that the trinity doctrine was due to progressive revelation to their church. It was not official church doctrine until hundreds of years after the death of Christ.
That explains why Paul, in every letter he wrote that can be attributed to him, only sent greetings from the divine members of the Godhead, the father and son:
Rom 1:7 To all who are in Rome, beloved of God, called to be saints: Grace to you and peace from God our Father and the Lord Jesus Christ.
1Co 1:3 Grace to you and peace from God our Father and the Lord Jesus Christ.
2Co 1:2 Grace to you and peace from God our Father and the Lord Jesus Christ.
Gal 1:3 Grace to you and peace from God the Father and our Lord Jesus Christ,
Eph 1:2 Grace to you and peace from God our Father and the Lord Jesus Christ.
Php 1:2 Grace to you and peace from God our Father and the Lord Jesus Christ.
Col 1:2 To the saints and faithful brethren in Christ who are in Colosse: Grace to you and peace from God our Father and the Lord Jesus Christ.
1Th 1:1 Paul, Silvanus, and Timothy, To the church of the Thessalonians in God the Father and the Lord Jesus Christ: Grace to you and peace from God our Father and the Lord Jesus Christ.
2Th 1:2 Grace to you and peace from God our Father and the Lord Jesus Christ.
1Ti 1:2 To Timothy, a true son in the faith: Grace, mercy, and peace from God our Father and Jesus Christ our Lord.
2Ti 1:2 To Timothy, a beloved son: Grace, mercy, and peace from God the Father and Christ Jesus our Lord.
Tit 1:4 To Titus, a true son in our common faith: Grace, mercy, and peace from God the Father and the Lord Jesus Christ our Savior.
Phm 1:3 Grace to you and peace from God our Father and the Lord Jesus Christ.
This would be quite an oversight if Paul believe there was a person called "the holy spirit" in the Godhead. But he didn't believe this because he knew that scripture doesn't record it.
There are many quotes by Paul (as well as our Lord) referring to the Holy Spirit as a person:
1Co_2:12 Now we have received not the spirit of the world, but the Spirit who is from God, that we might understand the things freely given us by God.
Paul refers to the Spirit as a person and this person ("who") comes from God the Father. Paul signs off his letter to the Corinthians properly referring to all three:
This, btw, is WHY it is important to study the teachings of those who come before us as well as the scriptures; to avoid serious errors like this.