In fact, speaking of Islam in the aggregate I think that they qualify as "antichrist" because of what John says in that epistle.
“I didn’t say any Muslim hath the Father.”
No, but your question was, can they being worshiping Him falsely?
I think that verse refutes that idea. They may be worshipping something, but if they don’t have the Son, then they are not worshiping the Father.
A similar idea is expressed in John 8, in more detailed fashion by Christ while talking with the Jews who also claimed to worship the “God of Abraham”:
31To the Jews who had believed him, Jesus said, If you hold to my teaching, you are really my disciples. 32Then you will know the truth, and the truth will set you free.
33They answered him, We are Abrahams descendants and have never been slaves of anyone. How can you say that we shall be set free?
34Jesus replied, Very truly I tell you, everyone who sins is a slave to sin. 35Now a slave has no permanent place in the family, but a son belongs to it forever. 36So if the Son sets you free, you will be free indeed. 37I know that you are Abrahams descendants. Yet you are looking for a way to kill me, because you have no room for my word. 38I am telling you what I have seen in the Fathers presence, and you are doing what you have heard from your father.b
39Abraham is our father, they answered.
If you were Abrahams children, said Jesus, then you wouldc do what Abraham did. 40As it is, you are looking for a way to kill me, a man who has told you the truth that I heard from God. Abraham did not do such things. 41You are doing the works of your own father.
We are not illegitimate children, they protested. The only Father we have is God himself.
42Jesus said to them, If God were your Father, you would love me, for I have come here from God. I have not come on my own; God sent me. 43Why is my language not clear to you? Because you are unable to hear what I say. 44You belong to your father, the devil, and you want to carry out your fathers desires. He was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies. 45Yet because I tell the truth, you do not believe me! 46Can any of you prove me guilty of sin? If I am telling the truth, why dont you believe me? 47Whoever belongs to God hears what God says. The reason you do not hear is that you do not belong to God.
If the Muslims belonged to God, they would hear Jesus’ words and follow them. Clearly they do not.