The bible clearly teaches that there is only one God, yet all three Persons are called God.
There is only one God:
Hear, O Israel: The LORD our God is one LORD. (Deuteronomy 6:4)
Before me there was no God formed, neither shall there be after me. (Is. 43:10)
The Father is God:
Grace unto you, and peace, from God our Father and the Lord Jesus Christ. (2 Thessalonians 1:2)
The Son is God:
The Word was God. (John 1:1-5, 14) Jesus is identified as "the Word."
I and the Father are one. (John 10:30-33)
Jesus' disciple Thomas addressed Jesus as "My Lord and my God." (John 20:28)
Jesus did not tell Thomas he was mistaken; instead Jesus accepted these titles. Other people in Scripture, notably Paul and Barnabas (Acts 14), refused to accept worship as gods.
But unto the Son he saith, Thy throne, O God, is for ever and ever: a sceptre of righteousness is the sceptre of thy kingdom. (Hebrews 1:8)
Wherefore God also hath highly exalted him, and given him a name which is above every name: That at the name of Jesus every knee should bow, of things in heaven, and things of earth, and things under the earth; and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father. (Philippians 2:9-11)
See these passages about Jesus' deity: Isaiah 7:14; Isaiah 9:6; John 1:1; John 1:18; John 8:58-59; John 10:30; Acts 20:28; Romans 9:5 & 10:9-13; Colossians 1:15-16; Colossians 2:9; Titus 2:13; Hebrews 1:3,8; 2 Peter 1:1; 1 John 5:20.
The Holy Spirit is God:
But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost?...Thou hast not lied unto men, but unto God. (acts 5:3-4)
Now the Lord is that Spirit. (2 Corinthians 3:17)
"The Lord" here refers to "the LORD" in the Old Testament verse (exodus 34:34) Paul had just quoted in the previous verse (2 Corinthians 3:16)