While I believe that Dale M's answer is correct, the Sage Advice Compendium (page 18) also clarifies:

Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

 

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

Since the answer is No to each of the questions, a Paladin's aura would not be considered magical.

While I believe that Dale M's answer is correct, the Sage Advice Compendium (page 18) also clarifies:

Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

Since the answer is No to each of the questions, a Paladin's aura would not be considered magical.

While I believe that Dale M's answer is correct, the Sage Advice Compendium (page 17) also clarifies:

Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

Since the answer is No to each of the questions, a Paladin's aura would not be considered magical.

While I believe that Dale M's answer is correct, the Sage Advice Compendium (page 18) also clarifies:

Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

Since the answer is No to each of the questions, a Paladin's aura would not be considered magical.