While Jehovah's Witnesses are often labeled as modern-day Arians due to their shared non-Trinitarian views, the two systems differ significantly in their specific doctrines.
Jehovah's Witnesses believe Jesus can fully know the Father, whereas Arius denied this; additionally, Witnesses view the Holy Spirit as an impersonal active force, while Arius considered the Holy Spirit to be a high-ranking angelic person.
Jehovah Witnesses (JW) are often referred to as 'modern-day Arians'. While there are similarities in theology and doctrine, the JW differ from Arians in the following ways:
JW believe Jesus can fully know the Father (something Arius himself denied)
JW consider the Holy Spirit to be God's 'active force' or 'energy', which had no beginning, and is not an actual person
Arius considered the Holy Spirit to be a person or a high-ranking angel, which had a beginning as a creature
JW pray to God, through Jesus as a mediator. Arians prayed directly to Jesus